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<!doctype html>
<html>
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<title>java-cvika</title><link href='https://fonts.loli.net/css?family=Open+Sans:400italic,700italic,700,400&subset=latin,latin-ext' rel='stylesheet' type='text/css' /><style type='text/css'>html {overflow-x: initial !important;}:root { --bg-color: #ffffff; --text-color: #333333; --select-text-bg-color: #B5D6FC; --select-text-font-color: auto; --monospace: "Lucida Console",Consolas,"Courier",monospace; }
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<div id='write' class = 'is-mac'><h1><a name="java-úkoly-ze-cvičení" class="md-header-anchor"></a><span>Java (úkoly ze cvičení)</span></h1><p><span>Násedují úkoly ze cvičení (2019/2020), kde to bylo možné tak se správnou odpovědí a vysvětlením. Důležité příklady, které bývají na zkouškách, jsou označeny jako </span><em><span>zkouškový příklad</span></em><span>.</span></p><h2><a name="cvičení-1" class="md-header-anchor"></a><span>Cvičení 1</span></h2><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable-3">Integer</span> <span class="cm-variable">i1</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable-3">Integer</span>(<span class="cm-number">1</span>);</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable-3">Integer</span> <span class="cm-variable">i2</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable-3">Integer</span>(<span class="cm-number">1</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">if</span> (<span class="cm-variable">i1</span> <span class="cm-operator">==</span> <span class="cm-variable">i2</span>)</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"ANO"</span>); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">else</span> </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"NE"</span>);</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 132px;"></div><div class="CodeMirror-gutters" style="display: none; height: 132px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> NE</span></p><p><code>==</code><span> porovnává pro referenční typy (což jsou všechny objekty, i </span><code>Integer</code><span>) pouze ukazatele do paměti, ne hodnoty. </span><code>i1</code><span> a </span><code>i2</code><span> jsou v tomto případě různé objekty s různými pozicemi v paměti.</span></p><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Overflow</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">b</span> <span class="cm-operator">=</span> <span class="cm-number">2147483647</span>; </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">b</span>); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">b</span> <span class="cm-operator">=</span> <span class="cm-variable">b</span> <span class="cm-operator">+</span> <span class="cm-number">1</span>; </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">b</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> } </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 176px;"></div><div class="CodeMirror-gutters" style="display: none; height: 176px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> 2147483647 -2147483648</span></p><p><span>2147483647 je Integer.MAX_VALUE, když k ní přičteme jedničku, dojde k </span><em><span>overflow</span></em><span> (jede se opět "od začátku" intu).</span></p><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">class</span> <span class="cm-def">URL</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"url:"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">http</span>:<span class="cm-comment">//google.com/</span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">":url"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 154px;"></div><div class="CodeMirror-gutters" style="display: none; height: 154px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> url: :url</span></p><p><span>V </span><code>http://google.com/</code><span> se vše po </span><code>//</code><span> bere jako komentář a </span><code>http:</code><span> se bere jako label. Labely fungují podobně jako v Pascalu, lze na ně skočit pomocí </span><code>continue</code><span>.</span></p><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Swap</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">x</span> <span class="cm-operator">=</span> <span class="cm-number">10</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">y</span> <span class="cm-operator">=</span> <span class="cm-number">20</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">x</span> <span class="cm-variable">^</span><span class="cm-operator">=</span> <span class="cm-variable">y</span> <span class="cm-variable">^</span><span class="cm-operator">=</span> <span class="cm-variable">x</span> <span class="cm-variable">^</span><span class="cm-operator">=</span> <span class="cm-variable">y</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">x</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">y</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 198px;"></div><div class="CodeMirror-gutters" style="display: none; height: 198px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> 0 10</span></p><p><code>a ^= b</code><span> odpovídá </span><code>a = a ^ b</code><span>. </span><code>a ^ b</code><span> je operace bitwise </span><code>XOR</code><span>, při níž se </span><code>a</code><span> a </span><code>b</code><span> berou jako bity (čili pokud to jsou integery, berou se převedené do binární soustavy). Kratší z nich se zepředu doplní nulami, aby byla obě čísla stejně dlouhá. Poté se porovná i-tý bit z </span><code>a</code><span> s i-tým bitem z </span><code>b</code><span> pomocí operace XOR. </span></p><p><code>x ^= y ^= x ^= y</code><span> lze pak přepsat jako </span><code>x = x ^ (y = y ^ (x = x ^ y))</code><span>, což je výraz, který se vyhodnocuje zleva. Po dosazení vyjde </span><code>x = 10 ^ (y = 20 ^ (x = 10 ^ y))</code><span> atd.</span></p><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">class</span> <span class="cm-def">ForCycle</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">j</span> <span class="cm-operator">=</span> <span class="cm-number">0</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">for</span> (<span class="cm-variable-3">int</span> <span class="cm-variable">i</span> <span class="cm-operator">=</span> <span class="cm-variable-3">Integer</span>.<span class="cm-variable">MAX_VALUE</span> <span class="cm-operator">-</span> <span class="cm-number">10</span>; <span class="cm-variable">i</span> <span class="cm-operator"><=</span> <span class="cm-variable-3">Integer</span>.<span class="cm-variable">MAX_VALUE</span>; <span class="cm-variable">i</span><span class="cm-operator">++</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">j</span><span class="cm-operator">++</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">j</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 198px;"></div><div class="CodeMirror-gutters" style="display: none; height: 198px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Nekonečný cyklus (nevypíše se nic)</span></p><p><code>int i</code><span> nikdy nebude větší než </span><code>Integer.MAX_VALUE</code><span>, protože je to jeho horní hranice.</span></p><h2><a name="cvičení-2" class="md-header-anchor"></a><span>Cvičení 2</span></h2><p><strong><span>Doplňte deklaraci </span><code>i</code><span>, aby se vypsalo </span><code>ANO</code></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">if</span> (<span class="cm-variable">i</span> <span class="cm-operator">==</span> <span class="cm-operator">-</span><span class="cm-variable">i</span> <span class="cm-operator">&&</span> <span class="cm-variable">i</span> <span class="cm-operator">!=</span> <span class="cm-number">0</span>) { </span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">“ANO“</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">} <span class="cm-keyword">else</span> { </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">“NE“</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 110px;"></div><div class="CodeMirror-gutters" style="display: none; height: 110px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> </span><code>i = Integer.MIN_VALUE</code><span> </span></p><p><span>Když ho znegujeme, dostaneme </span><code>Integer.MAX_VALUE + 1</code><span>, což je zase </span><code>Integer.MIN_VALUE</code><span>.</span></p><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre>x</pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">LoopTest</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) {</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable-3">int</span> <span class="cm-variable">START</span> <span class="cm-operator">=</span> <span class="cm-number">2000000000</span>;</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable-3">int</span> <span class="cm-variable">count</span> <span class="cm-operator">=</span> <span class="cm-number">0</span>;</span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">for</span> (<span class="cm-keyword">float</span> <span class="cm-variable">f</span> <span class="cm-operator">=</span> <span class="cm-variable">START</span>; <span class="cm-variable">f</span> <span class="cm-operator"><</span> <span class="cm-variable">START</span> <span class="cm-operator">+</span> <span class="cm-number">50</span>; <span class="cm-variable">f</span><span class="cm-operator">++</span>) {</span></pre></div><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">count</span><span class="cm-operator">++</span>;</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">count</span>); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 220px;"></div><div class="CodeMirror-gutters" style="display: none; height: 220px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> 0</span></p><p><span>Má to co dočinění s </span><em><span>floating-point</span></em><span> čísly. </span><code>START</code><span> je sice na začátku </span><code>int</code><span>, kvůli porovnání s </span><code>f</code><span> je však převeden na </span><code>float</code><span>. </span><code>START</code><span> jen o málo menší než </span><span class="MathJax_SVG" tabindex="-1" style="font-size: 100%; display: inline-block;"><svg xmlns:xlink="http://www.w3.org/1999/xlink" width="3.036ex" height="2.344ex" viewBox="0 -956.9 1307.1 1009.2" role="img" focusable="false" style="vertical-align: -0.121ex;"><defs><path stroke-width="0" id="E8-MJMAIN-32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315T301 241Q265 210 201 149L142 93L218 92Q375 92 385 97Q392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19V31Q50 38 56 46T86 81Q115 113 136 137Q145 147 170 174T204 211T233 244T261 278T284 308T305 340T320 369T333 401T340 431T343 464Q343 527 309 573T212 619Q179 619 154 602T119 569T109 550Q109 549 114 549Q132 549 151 535T170 489Q170 464 154 447T109 429Z"></path><path stroke-width="0" id="E8-MJMAIN-33" d="M127 463Q100 463 85 480T69 524Q69 579 117 622T233 665Q268 665 277 664Q351 652 390 611T430 522Q430 470 396 421T302 350L299 348Q299 347 308 345T337 336T375 315Q457 262 457 175Q457 96 395 37T238 -22Q158 -22 100 21T42 130Q42 158 60 175T105 193Q133 193 151 175T169 130Q169 119 166 110T159 94T148 82T136 74T126 70T118 67L114 66Q165 21 238 21Q293 21 321 74Q338 107 338 175V195Q338 290 274 322Q259 328 213 329L171 330L168 332Q166 335 166 348Q166 366 174 366Q202 366 232 371Q266 376 294 413T322 525V533Q322 590 287 612Q265 626 240 626Q208 626 181 615T143 592T132 580H135Q138 579 143 578T153 573T165 566T175 555T183 540T186 520Q186 498 172 481T127 463Z"></path><path stroke-width="0" id="E8-MJMAIN-31" d="M213 578L200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641T273 663Q275 666 285 666Q294 666 302 660V361L303 61Q310 54 315 52T339 48T401 46H427V0H416Q395 3 257 3Q121 3 100 0H88V46H114Q136 46 152 46T177 47T193 50T201 52T207 57T213 61V578Z"></path></defs><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="matrix(1 0 0 -1 0 0)"><use xlink:href="#E8-MJMAIN-32" x="0" y="0"></use><g transform="translate(500,392)"><use transform="scale(0.707)" xlink:href="#E8-MJMAIN-33"></use><use transform="scale(0.707)" xlink:href="#E8-MJMAIN-31" x="500" y="0"></use></g></g></svg></span><script type="math/tex">2^{31}</script><span>, proto v jeho binárním zápisu bude určitě 31. bit jednička. </span><code>float</code><span> čísla jsou sice 32 bitová, ale 1 bit z toho je na znaménko, dalších 8 je na exponent a tak na samotné číslo zbude pouze 23 bitů. </span></p><p><span>Protože k uložení start potřebujeme mít 31. bit nastavený na 1, při převodu na </span><code>float</code><span> si ze </span><code>START</code><span> necháme následujících 23 bitů: [31., 30., 29., ..., 8.] — jinými slovy prvních sedm bitů ze </span><code>START</code><span> odstřihneme, neboť se nám do floatu nevlezou. Protože přičtená 50 se vleze do prvních sedmi bitů, a my těchto sedm bitů poté odstřihneme, přičtení 50 se vůbec neprojeví a platí </span><code>START == f == START + 50</code><span> (pokud je </span><code>START</code><span> převeden na </span><code>float</code><span>).</span></p><h2><a name="cvičení-3" class="md-header-anchor"></a><span>Cvičení 3</span></h2><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Test01</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">test</span>()); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">boolean</span> <span class="cm-variable">test</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">try</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">return</span> <span class="cm-atom">true</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span>} <span class="cm-keyword">finally</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">return</span> <span class="cm-atom">false</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span>} </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 264px;"></div><div class="CodeMirror-gutters" style="display: none; height: 264px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> </span><code>false</code></p><p><code>finally</code><span> přebíjí většinu věcí, i </span><code>return</code><span>.</span></p><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Test01</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">try</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Hello world!"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">exit</span>(<span class="cm-number">0</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span>} <span class="cm-keyword">finally</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Goodbye"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span>}</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 220px;"></div><div class="CodeMirror-gutters" style="display: none; height: 220px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> "Hello world!"</span></p><p><code>finally</code><span> přebíjí většinu věcí, ale </span><code>System.exit()</code><span> je jedna z výjimek — prostě rovnou ukončí průběh programu. Kromě něj takto funguje i </span><code>halt</code><span> a pak už většinou jen pády JVM nebo samotného operačního systému.</span></p><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">class</span> <span class="cm-def">ParamsTest</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable">ParamsTest</span>(<span class="cm-variable-3">Object</span> <span class="cm-variable">o</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"ParamsTest(Object o)"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable">ParamsTest</span>(<span class="cm-variable-3">long</span>[] <span class="cm-variable">a</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"ParamsTest(long[] a)"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">new</span> <span class="cm-variable">ParamsTest</span>(<span class="cm-atom">null</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 242px;"></div><div class="CodeMirror-gutters" style="display: none; height: 242px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> ParamsTest(long[] a)</span></p><p><span>Podle skutečných parametrů se vybere ta nejspecifičtější vyhovující implementace (zde </span><code>long[] a</code><span>).</span></p><p><strong><span>Co se vypíše?</span></strong><span> (zkouškový příklad)</span></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><span><span></span>x</span></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">class</span> <span class="cm-def">A</span> { </span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">x</span> <span class="cm-operator">=</span> <span class="cm-number">1</span>; </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">} </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text=""></span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">class</span> <span class="cm-def">B</span> <span class="cm-keyword">extends</span> <span class="cm-variable">A</span> { </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">int</span> <span class="cm-variable">x</span> <span class="cm-operator">=</span> <span class="cm-number">2</span>; </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable-3">void</span> <span class="cm-variable">foo</span>() { </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-keyword">this</span>.<span class="cm-variable">x</span>); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-keyword">super</span>.<span class="cm-variable">x</span>); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(((<span class="cm-variable">A</span>)<span class="cm-keyword">this</span>).<span class="cm-variable">x</span>); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> } </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) { </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">B</span> <span class="cm-variable">b</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">B</span>(); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">b</span>.<span class="cm-variable">foo</span>(); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> } </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 352px;"></div><div class="CodeMirror-gutters" style="display: none; height: 352px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> 2 1 1</span></p><p><span>Statické metody se koukají pouze na typ objektu, ne na jeho hodnotu; podle toho se pak zavolá konkrétní implementace. Viz také </span><a href='https://stackoverflow.com/questions/60065506/inherited-attribute-method-static-method-behavior?noredirect=1'><span>tato otázka na Stack Overflow</span></a><span>.</span></p><h2><a name="cvičení-4" class="md-header-anchor"></a><span>Cvičení </span><strong><span>4</span></strong></h2><p><strong><span>Co program udělá?</span></strong><span> (zkouškový příklad)</span></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Null</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> ((<span class="cm-variable">Null</span>) <span class="cm-atom">null</span>).<span class="cm-variable">hello</span>(); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">hello</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Hello world!"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span>} </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 176px;"></div><div class="CodeMirror-gutters" style="display: none; height: 176px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> vypíše se "Hello world!"</span></p><p><span>Že se třída jmenuje </span><code>Null</code><span> je v pořádku. Poté sice voláme </span><code>null.hello()</code><span>, ale </span><code>hello()</code><span> je statická metoda, čili vůbec nekouká na reálnou hodnotu objektu — pouze na jeho typ (a to je </span><code>Null</code><span>). Vše tedy funguje, jak má.</span></p><p><strong><span>Co program udělá?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">class</span> <span class="cm-def">Test01</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">run</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Konec"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text=""></span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">run</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">try</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">run</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> } <span class="cm-keyword">finally</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">run</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 308px;"></div><div class="CodeMirror-gutters" style="display: none; height: 308px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Myslím, že vyhodí </span><code>StackOverflowError</code><span>.</span></p><p><strong><span>Co program vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">class</span> <span class="cm-def">A</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-variable-3">String</span> <span class="cm-variable">className</span> <span class="cm-operator">=</span> <span class="cm-string">"A"</span>; </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text=""></span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">class</span> <span class="cm-def">B</span> <span class="cm-keyword">extends</span> <span class="cm-variable">A</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">private</span> <span class="cm-variable-3">String</span> <span class="cm-variable">className</span> <span class="cm-operator">=</span> <span class="cm-string">"B"</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text=""></span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Test02</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-keyword">new</span> <span class="cm-variable">B</span>().<span class="cm-variable">className</span>); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 286px;"></div><div class="CodeMirror-gutters" style="display: none; height: 286px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Nepřeloží se, ve třídě Test02 je chyba.</span></p><p><span>Deklarace </span><code>className</code><span> v </span><code>B</code><span> schová atribut </span><code>className</code><span> z </span><code>A</code><span> (doslova se to jmenuje </span><em><span>field hiding</span></em><span>). To, že je sama </span><code>private</code><span> na věci nic nemění. Protože původní </span><code>className</code><span> z </span><code>A</code><span> je schovaná a </span><code>className</code><span> z </span><code>B</code><span> je zase </span><code>private</code><span>, je chyba vůbec se snažit tohoto atributu dosáhnout.</span></p><h2><a name="cvičení-5" class="md-header-anchor"></a><span>Cvičení 5</span></h2><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">interface</span> <span class="cm-def">Test</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Hello"</span>); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 110px;"></div><div class="CodeMirror-gutters" style="display: none; height: 110px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Je to úplně v pořádku, vypíše se Hello.</span></p><p><span>V interfacu mohou totiž být i statické metody.</span></p><p><strong><span>Co se vypíše?</span></strong><span> (zkouškový příklad)</span></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">enum</span> <span class="cm-def">Test</span> { </span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">RED</span>, <span class="cm-variable">GREEN</span>, <span class="cm-variable">BLUE</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text=""></span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) { </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Hello"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 154px;"></div><div class="CodeMirror-gutters" style="display: none; height: 154px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Je to úplně v pořádku, vypíše se Hello.</span></p><p><code>enum</code><span> je v podstatě jen vylepšená třída, proto může obsahovat statické metody. Nemůže však dědit, neboť implicitně již dědí od </span><code>java.lang.Enum</code><span>. Může dokonce obsahovat i abstraktní metody, pak je ale musí implementovat každý z prvků enumu.</span></p><h2><a name="cvičení-6" class="md-header-anchor"></a><span>Cvičení 6</span></h2><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Greeter</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span> (<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable-3">String</span> <span class="cm-variable">greeting</span> <span class="cm-operator">=</span> <span class="cm-string">"Hello world"</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">for</span> (<span class="cm-variable-3">int</span> <span class="cm-variable">i</span> <span class="cm-operator">=</span> <span class="cm-number">0</span>; <span class="cm-variable">i</span> <span class="cm-operator"><</span> <span class="cm-variable">greeting</span>.<span class="cm-variable">length</span>(); <span class="cm-variable">i</span><span class="cm-operator">++</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">write</span>(<span class="cm-variable">greeting</span>.<span class="cm-variable">charAt</span>(<span class="cm-variable">i</span>)); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span>} </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 176px;"></div><div class="CodeMirror-gutters" style="display: none; height: 176px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Nevypíše se nic.</span></p><p><code>PrintStream.write()</code><span> sice na stream přidá dané znaky, ale stream pak automaticky nevyprázdní do konzole — proto nejde nic vidět. Naproti tomu </span><code>println()</code><span> se o toto stará, čili kdybychom za loop přidali </span><code>System.out.println("");</code><span>, vypsalo by se už </span><code>Hello world</code><span>.</span></p><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">class</span> <span class="cm-def">Slasher</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">argv</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">String</span> <span class="cm-variable">fullClassName</span> <span class="cm-operator">=</span> <span class="cm-string">"cz.cuni.mff.java.io.Slasher"</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">String</span> <span class="cm-variable">fileName</span> <span class="cm-operator">=</span> <span class="cm-variable">fullClassName</span>.<span class="cm-variable">replaceAll</span>(<span class="cm-string">"."</span>, <span class="cm-string">"/"</span>) <span class="cm-operator">+</span> <span class="cm-string">".java"</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Trida "</span> <span class="cm-operator">+</span> <span class="cm-variable">fullClassName</span> <span class="cm-operator">+</span> <span class="cm-string">" musi byt v souboru "</span> <span class="cm-operator">+</span> <span class="cm-variable">fileName</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 154px;"></div><div class="CodeMirror-gutters" style="display: none; height: 154px;"></div></div></div></pre><p><em><span>Řešení</span></em><span>: Trida cz.cuni.mff.java.io.Slasher musi byt v souboru ///////////////////////////.java</span></p><p><code>String.replaceAll()</code><span> bere jako první argument </span><code>regex</code><span>, ne obyčejný string. Proto </span><code>.</code><span> je interpretováno regex enginem jako "jakýkoli znak" a všechny znaky jsou proto nahrazeny lomítkem.</span></p><h2><a name="cvičení-7" class="md-header-anchor"></a><span>Cvičení 7</span></h2><p><strong><span>Co program udělá?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">TestString</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">String</span> <span class="cm-variable">s</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable-3">String</span>(<span class="cm-string">"Hello world"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">s</span>); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text=""></span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">class</span> <span class="cm-variable-3">String</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">private</span> <span class="cm-keyword">final</span> <span class="cm-variable">java</span>.<span class="cm-variable">lang</span>.<span class="cm-variable-3">String</span> <span class="cm-variable">s</span>; </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable-3">String</span>(<span class="cm-variable">java</span>.<span class="cm-variable">lang</span>.<span class="cm-variable-3">String</span> <span class="cm-variable">s</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">this</span>.<span class="cm-variable">s</span> <span class="cm-operator">=</span> <span class="cm-variable">s</span>; </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable">java</span>.<span class="cm-variable">lang</span>.<span class="cm-variable-3">String</span> <span class="cm-variable">toString</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">return</span> <span class="cm-variable">s</span>; </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 352px;"></div><div class="CodeMirror-gutters" style="display: none; height: 352px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Přeloží se, ale při runtimu vyhodí chybu, že mu chybí metoda </span><code>main</code><span>.</span></p><p><code>main</code><span> má totiž v této chvíli mít hlavičku </span><code>public static void main(java.lang.String[] args)</code><span>, protože </span><code>String</code><span> je teď ta naše nová třída a ne původní </span><code>String</code><span>.</span></p><p><strong><span>Lze třídu </span><code>B</code><span> nadeklarovat tak, aby program vypsal </span><code>false</code><span>? (bez přepsání </span><code>equals</code><span>)</span></strong><span> </span></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">A</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">B</span> <span class="cm-variable">b</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">B</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">b</span>.<span class="cm-variable">equals</span>(<span class="cm-variable">b</span>)); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 132px;"></div><div class="CodeMirror-gutters" style="display: none; height: 132px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Ano, ale je to dost podvod.</span></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">class</span> <span class="cm-def">B</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable">B</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-atom">false</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">exit</span>(<span class="cm-number">0</span>); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 132px;"></div><div class="CodeMirror-gutters" style="display: none; height: 132px;"></div></div></div></pre><h2><a name="cvičení-8" class="md-header-anchor"></a><span>Cvičení 8</span></h2><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Test01</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-keyword">synchronized</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">a</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">Thread</span> <span class="cm-variable">t</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">Thread</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable-3">void</span> <span class="cm-variable">run</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">pong</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> };</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">t</span>.<span class="cm-variable">start</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Ping"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text=""></span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">static</span> <span class="cm-keyword">synchronized</span> <span class="cm-variable-3">void</span> <span class="cm-variable">pong</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Pong"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 330px;"></div><div class="CodeMirror-gutters" style="display: none; height: 330px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Ping Pong</span></p><p><span>Obě metody jsou </span><code>static synchronized</code><span>, čili berou zámek přímo od třídy </span><code>Test01</code><span>. Když už jsme v </span><code>main</code><span>, má současné vlákno zámek (protože vstoupilo do </span><code>synchronized</code><span> bloku) a tak se vlákno </span><code>t</code><span> (potažmo metoda </span><code>pong()</code><span>) spustí až poté, co skončí to naše vlákno.</span></p><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">class</span> <span class="cm-def">SelfInterruption</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">Thread</span>.<span class="cm-variable">currentThread</span>().<span class="cm-variable">interrupt</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">if</span> (<span class="cm-variable">Thread</span>.<span class="cm-variable">interrupted</span>()) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Interrupted: "</span> <span class="cm-operator">+</span> <span class="cm-variable">Thread</span>.<span class="cm-variable">interrupted</span>());</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> } <span class="cm-keyword">else</span> {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"Not interrupted: "</span> <span class="cm-operator">+</span> <span class="cm-variable">Thread</span>.<span class="cm-variable">interrupted</span>());</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 220px;"></div><div class="CodeMirror-gutters" style="display: none; height: 220px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Interrupted: false</span></p><p><code>Thread.interrupted()</code><span> totiž nejen vrátí současnou hodnotu </span><code>.interrupted()</code><span>, ale také ji resetuje na </span><code>false</code><span>. Kdyby se místo toho použilo </span><code>this.isInterrupted()</code><span>, který po vrácení žádný reset neprovádí, vypsalo by se </span><em><span>Interrupted: true</span></em><span>.</span></p><h2><a name="cvičení-9" class="md-header-anchor"></a><span>Cvičení 9</span></h2><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java" style="break-inside: unset;"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Test01</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">private</span> <span class="cm-keyword">static</span> <span class="cm-variable">java</span>.<span class="cm-variable">util</span>.<span class="cm-variable">Random</span> <span class="cm-variable">rnd</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">java</span>.<span class="cm-variable">util</span>.<span class="cm-variable">Random</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text=""></span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable-3">StringBuffer</span> <span class="cm-variable">word</span> <span class="cm-operator">=</span> <span class="cm-atom">null</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">switch</span> (<span class="cm-variable">rnd</span>.<span class="cm-variable">nextInt</span>(<span class="cm-number">2</span>)) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">case</span> <span class="cm-number">1</span>:</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">word</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable-3">StringBuffer</span>(<span class="cm-string">'P'</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">case</span> <span class="cm-number">2</span>:</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">word</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable-3">StringBuffer</span>(<span class="cm-string">'G'</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">default</span>:</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">word</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable-3">StringBuffer</span>(<span class="cm-string">'M'</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">word</span>.<span class="cm-variable">append</span>(<span class="cm-string">'a'</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">word</span>.<span class="cm-variable">append</span>(<span class="cm-string">'i'</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">word</span>.<span class="cm-variable">append</span>(<span class="cm-string">'n'</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">word</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 418px;"></div><div class="CodeMirror-gutters" style="display: none; height: 418px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> ain</span></p><p><span>V </span><code>case</code><span> nejsou breaky, takže word je vždy nakonec nastaven na </span><code>new StringBuffer('M')</code><span>. Protože </span><code>StringBuffer</code><span> dostal </span><code>char</code><span> (potažmo </span><code>int</code><span>) bere to jako hranici kapacity (ne jako první písmeno — to by musel dostat </span><code>"M"</code><span>).</span></p><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Test02</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span> <span class="cm-variable">args</span>[]) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">"H"</span> <span class="cm-operator">+</span> <span class="cm-string">"a"</span>);</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-string">'H'</span> <span class="cm-operator">+</span> <span class="cm-string">'a'</span>); </span></pre><div class="" style="position: relative;"><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 132px;"></div><div class="CodeMirror-gutters" style="display: none; height: 132px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Ha 169</span></p><p><code>char</code><span> + </span><code>char</code><span> je v tomto případě interpretováno jako součet intů. Pro zajímavost, </span><code>println("" + 'H' + 'a')</code><span> by vypsalo skutečně </span><code>Ha</code><span> [</span><a href='https://www.destroyallsoftware.com/talks/wat'><em><span>laughs in javascript</span></em></a><span>].</span></p><h2><a name="cvičení-10" class="md-header-anchor"></a><span>Cvičení 10</span></h2><p><strong><span>Lze definovat </span><code>i</code><span> tak, aby byl cyklus nekonečný?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">while</span> (<span class="cm-variable">i</span> <span class="cm-operator">!=</span> <span class="cm-variable">i</span>) { }</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 22px;"></div><div class="CodeMirror-gutters" style="display: none; height: 22px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Ano, </span><code>Double.NaN</code><span> se nerovná ničemu, ani sám sobě.</span></p><p><strong><span>Co se vypíše?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Increment</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-variable-3">void</span> <span class="cm-variable">main</span>(<span class="cm-variable-3">String</span>[] <span class="cm-variable">args</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable-3">int</span> <span class="cm-variable">j</span> <span class="cm-operator">=</span> <span class="cm-number">0</span>;</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">for</span> (<span class="cm-variable-3">int</span> <span class="cm-variable">i</span> <span class="cm-operator">=</span> <span class="cm-number">0</span>; <span class="cm-variable">i</span> <span class="cm-operator"><</span> <span class="cm-number">100</span>; <span class="cm-variable">i</span><span class="cm-operator">++</span>) {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">j</span> <span class="cm-operator">=</span> <span class="cm-variable">j</span><span class="cm-operator">++</span>; </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-variable">System</span>.<span class="cm-variable">out</span>.<span class="cm-variable">println</span>(<span class="cm-variable">j</span>); </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 198px;"></div><div class="CodeMirror-gutters" style="display: none; height: 198px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> 0</span></p><p><span>(Myslím, že) </span><code>j++</code><span> vrátí 0 a nastaví </span><code>j</code><span> na 1; </span><code>j = j++</code><span> pak vezme 0 z </span><code>j++</code><span> a uloží jí do </span><code>j</code><span>.</span></p><h2><a name="cvičení-11" class="md-header-anchor"></a><span>Cvičení 11</span></h2><p><strong><span>Lze od této třídy (bez použití reflection API) vytvořit další instance (kromě instance v atributu </span><code>INSTANCE</code><span>)?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Dog</span> <span class="cm-keyword">implements</span> <span class="cm-variable">Serializable</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-keyword">final</span> <span class="cm-variable">Dog</span> <span class="cm-variable">INSTANCE</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">Dog</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">private</span> <span class="cm-variable">Dog</span>() { }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-variable-3">String</span> <span class="cm-variable">toString</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">return</span> <span class="cm-string">"Woof"</span>; </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 154px;"></div><div class="CodeMirror-gutters" style="display: none; height: 154px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Leda bychom přidali něco do třídy samotné (jinak máme příklad tzv. </span><strong><span>singleton pattern</span></strong><span>, což je třída pouze s jednou instancí, zde konkrétně </span><code>INSTANCE</code><span>).</span></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation" style=""><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">public</span> <span class="cm-keyword">class</span> <span class="cm-def">Dog</span> <span class="cm-keyword">implements</span> <span class="cm-variable">Serializable</span> {</span></pre></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-keyword">static</span> <span class="cm-keyword">final</span> <span class="cm-variable">Dog</span> <span class="cm-variable">INSTANCE</span> <span class="cm-operator">=</span> <span class="cm-keyword">new</span> <span class="cm-variable">Dog</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">private</span> <span class="cm-variable">Dog</span>() { }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">public</span> <span class="cm-variable-3">String</span> <span class="cm-variable">toString</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-tab" role="presentation" cm-text=" "> </span><span class="cm-keyword">return</span> <span class="cm-string">"Woof"</span>; </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> </span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">public</span> <span class="cm-variable">Dog</span> <span class="cm-variable">getDog</span>() {</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> <span class="cm-keyword">return</span> <span class="cm-keyword">new</span> <span class="cm-variable">Dog</span>();</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"> }</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;">}</span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span cm-text=""></span></span></pre><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-variable">Dog</span> <span class="cm-variable">d</span> <span class="cm-operator">=</span> <span class="cm-variable">Dog</span>.<span class="cm-variable">getDog</span>();</span></pre></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 286px;"></div><div class="CodeMirror-gutters" style="display: none; height: 286px;"></div></div></div></pre><p><span>V tomto případě naopak používám tzv. </span><strong><span>factory pattern</span></strong><span> (máme metody, které nejsou konstruktory, ale přesto </span><em><span>vyrábějí</span></em><span> a vrací objekt své třídy).</span></p><h2><a name="cvičení-12" class="md-header-anchor"></a><span>Cvičení 12</span></h2><p><strong><span>Lze napsat deklaraci proměnné </span><code>i</code><span> tak, aby následující cyklus byl nekonečný?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">while</span> (<span class="cm-variable">i</span> <span class="cm-operator">!=</span> <span class="cm-variable">i</span> <span class="cm-operator">+</span> <span class="cm-number">0</span>) { }</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 22px;"></div><div class="CodeMirror-gutters" style="display: none; height: 22px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Ano, např. </span><code>String i = "a"</code><span>, potom </span><code>i + 0 == "a0"</code><span>.</span></p><p><strong><span>Lze napsat deklaraci proměnných </span><code>i</code><span> a </span><code>j</code><span> tak, aby následující cyklus byl nekonečný?</span></strong></p><pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="java"><div class="CodeMirror cm-s-inner CodeMirror-wrap" lang="java"><div style="overflow: hidden; position: relative; width: 3px; height: 0px; top: 0px; left: 8px;"><textarea autocorrect="off" autocapitalize="off" spellcheck="false" tabindex="0" style="position: absolute; bottom: -1em; padding: 0px; width: 1000px; height: 1em; outline: none;"></textarea></div><div class="CodeMirror-scrollbar-filler" cm-not-content="true"></div><div class="CodeMirror-gutter-filler" cm-not-content="true"></div><div class="CodeMirror-scroll" tabindex="-1"><div class="CodeMirror-sizer" style="margin-left: 0px; margin-bottom: 0px; border-right-width: 0px; padding-right: 0px; padding-bottom: 0px;"><div style="position: relative; top: 0px;"><div class="CodeMirror-lines" role="presentation"><div role="presentation" style="position: relative; outline: none;"><div class="CodeMirror-measure"><pre><span>xxxxxxxxxx</span></pre></div><div class="CodeMirror-measure"></div><div style="position: relative; z-index: 1;"></div><div class="CodeMirror-code" role="presentation"><div class="CodeMirror-activeline" style="position: relative;"><div class="CodeMirror-activeline-background CodeMirror-linebackground"></div><div class="CodeMirror-gutter-background CodeMirror-activeline-gutter" style="left: 0px; width: 0px;"></div><pre class=" CodeMirror-line " role="presentation"><span role="presentation" style="padding-right: 0.1px;"><span class="cm-keyword">while</span> (<span class="cm-variable">i</span> <span class="cm-operator"><=</span> <span class="cm-variable">j</span> <span class="cm-operator">&&</span> <span class="cm-variable">j</span> <span class="cm-operator"><=</span> <span class="cm-variable">i</span> <span class="cm-operator">&&</span> <span class="cm-variable">i</span> <span class="cm-operator">!=</span> <span class="cm-variable">j</span>) { }</span></pre></div></div></div></div></div></div><div style="position: absolute; height: 0px; width: 1px; border-bottom-width: 0px; border-bottom-style: solid; border-bottom-color: transparent; top: 22px;"></div><div class="CodeMirror-gutters" style="display: none; height: 22px;"></div></div></div></pre><p><em><span>Řešení:</span></em><span> Ano, například </span><code>i = new Integer(1)</code><span> a </span><code>j = new Integer(1)</code><span>.</span></p><p><span>Protože se jedná o referenční typy (objekty), výraz </span><code>i != j</code><span> je pravda, protože porovnává umístění v paměti a ne samotné hodnoty </span><code>i</code><span> a </span><code>j</code><span>.</span></p><p> </p></div>
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