Restructure examples and add basic tests

README.md

@@ -1,87 +1,131 @@
 # Java Examples Collection
 
-> Designed for the AUEB CS BSc Java Course
->> https://eclass.aueb.gr/courses/INF176/
+Designed for the AUEB CS BSc Java Course:
+https://eclass.aueb.gr/courses/INF176/
 
-This repository contains a collection of Java programming examples used for teaching core object-oriented programming (OOP) concepts in an engaging and applied way. Each example is organized as a separate package/module, and includes working code, documentation, and console interaction.
+This repository contains small, runnable Java examples and course projects used
+to teach core programming and object-oriented programming concepts. Topic-based
+examples live under `gr/aueb/cs/examples`, while larger mini-projects live under
+`gr/aueb/cs/projects`.
 
-## 📁 Project Structure
+## Project Structure
 
-Each top-level package contains a complete, runnable Java example:
+### `gr/aueb/cs/examples/introduction`
 
----
+Introductory Java examples covering variables, control flow, simple classes, and
+basic simulation.
 
-### 🎲 `montyhall/`
+### `gr/aueb/cs/examples/strings`
 
-A full implementation of the Monty Hall game:
+Examples for working with Java strings and common string operations.
 
-- OOP structure (`Door`, `MontyHallGame`, `Strategy`)
-- Interactive version (console-based)
-- Simulator to run thousands of trials
-- Visual comparison of strategies (switch vs stay)
+### `gr/aueb/cs/examples/inheritance`
 
-➡️ Teaches: classes, interfaces, composition, simulations, user interaction
+Examples for inheritance, `final`, dynamic binding, and polymorphism.
 
----
+### `gr/aueb/cs/examples/abstraction`
 
-### 🚶 `walkroutes/`
+Examples for abstract classes and salary-based employee models.
 
-A pedestrian routing system on a city grid:
+### `gr/aueb/cs/examples/interfaces`
 
-- Location graph representation
-- Obstacle-aware pathfinding
-- Modular packages: `model`, `routing`, `map`, `simulation`
+Small demonstrations of interfaces and interface-based design.
 
-➡️ Teaches: graphs, modular design, file input, BFS-style logic
+### `gr/aueb/cs/examples/collections`
 
----
+Examples using Java collections such as lists, queues, iterators, and traversal
+patterns.
 
-### 🎯 `demo/`
+### `gr/aueb/cs/examples/generics`
 
-Demonstrates the difference between:
+Examples for generic classes, generic methods, bounded type parameters,
+comparators, sorting, and type erasure.
 
-- `Math.random()` (static, simple, no seed)
-- `Random` class (object-based, supports seeding)
-- Repeatable pseudo-randomness
+### `gr/aueb/cs/examples/exceptions`
 
-➡️ Teaches: randomness, testing, debugging with seeded values
+Examples for exception handling, throwing exceptions, and safer error handling.
 
----
+### `gr/aueb/cs/examples/files`
 
-### 🏨 `hotelbooking/` *(optional extension)*
+Examples for reading and writing files, UTF-8 text, URLs, and CSV-style input.
 
-Simulates a basic hotel booking system with multiple room types.
+### `gr/aueb/cs/examples/unit`
 
-➡️ Teaches: inheritance, encapsulation, polymorphism
+A small calculator example with a matching unit test.
 
----
+### `gr/aueb/cs/examples/profiling`
 
-### 🎬 `movies/` *(optional extension)*
+Simple performance and profiling examples comparing data structures, primitive
+types, wrapper types, and buffer capacity choices.
 
-Loads movie reviews from a file and filters recommendations by genre, rating, or sentiment.
+### `gr/aueb/cs/examples/graphics`
 
-➡️ Teaches: file I/O, `ArrayList`, filtering, basic NLP
+Graphical Java examples, including a tag cloud visualization.
 
----
+### `gr/aueb/cs/examples/sound`
 
-## 🧪 How to Run
+Audio-related examples, including a simple alarm demo.
 
-Use the terminal or your favorite IDE (e.g., IntelliJ, Eclipse):
+### `gr/aueb/cs/examples/review`
+
+Review examples for dynamic dispatch, constructors, exceptions, anonymous
+classes, and randomness.
+
+### `gr/aueb/cs/projects`
+
+Larger examples and student-friendly mini-projects:
+
+- `montyhall`: Monty Hall game logic, strategies, console UI, and simulation.
+- `walkroute`: Walking route demos using linked structures, search, and agents.
+- `captcha`: A simple CAPTCHA generator and checker.
+- `javagotchi`: A virtual pet project.
+- `javagotchiWeb`: A Spring Boot web version of the Javagotchi project.
+
+## How to Run
+
+From the repository root, compile and run a single class by using its package
+path. For example:
 
 ```bash
-# Compile from src root
-javac montyhall/app/Main.java
-java montyhall.app.Main
+javac gr/aueb/cs/examples/introduction/Variables.java
+java gr.aueb.cs.examples.introduction.Variables
+```
+
+Another example:
+
+```bash
+javac gr/aueb/cs/examples/inheritance/Polymorphism.java
+java gr.aueb.cs.examples.inheritance.Polymorphism
+```
 
-# Or run another example
-javac demo/RandomComparison.java
-java demo.RandomComparison
+For examples that define multiple classes in the same package, compile the
+source file and then run the public class:
+
+```bash
+javac gr/aueb/cs/examples/interfaces/Demo.java
+java gr.aueb.cs.examples.interfaces.Demo
+```
+
+The Spring Boot project has its own README:
+
+```text
+gr/aueb/cs/projects/javagotchiWeb/README.md
+```
+
+## Running Tests
+
+The `gr/aueb/cs/examples/unit` package contains small JUnit 5 tests for the
+calculator example. Run them from the repository root with:
+
+```bash
+mvn test
 ```
 
-## ✏️ Contribution 
+## Contributing
 
-To contribute to this repo, [this cheatsheet](/git_cheatsheet.md) may help with the first steps. 
+To contribute to this repository, the [Git cheatsheet](git_cheatsheet.md) may
+help with the first steps.
 
-## 📄 License
+## License
 
 This project is licensed under the [MIT License](LICENSE).

gr/aueb/cs/abstraction/Employee.java → gr/aueb/cs/examples/abstraction/Employee.java

@@ -1,5 +1,5 @@
 
-package gr.aueb.cs.abstraction;
+package gr.aueb.cs.examples.abstraction;
 
 public abstract class Employee {
     private String firstName;

gr/aueb/cs/abstraction/JuniorSalariedEmployee.java → gr/aueb/cs/examples/abstraction/JuniorSalariedEmployee.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.abstraction;
+package gr.aueb.cs.examples.abstraction;
 
 abstract public class JuniorSalariedEmployee extends SalariedEmployee {
 

gr/aueb/cs/abstraction/SalariedEmployee.java → gr/aueb/cs/examples/abstraction/SalariedEmployee.java

@@ -1,5 +1,5 @@
 
-package gr.aueb.cs.abstraction;
+package gr.aueb.cs.examples.abstraction;
 
 public class SalariedEmployee extends Employee {
     private double weeklySalary;

gr/aueb/cs/collections/CollectionTest.java → gr/aueb/cs/examples/collections/CollectionTest.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.collections;
+package gr.aueb.cs.examples.collections;
 // // Based on the example in the book of Deitel (pp 834, 9th edition)
 // https://github.com/pdeitel/JavaHowToProgram11e_EarlyObjects/blob/7bf604beb846d3bb99b52d8b330da5e354a0224a/examples/ch16/fig16_02/CollectionTest.java
 // Collection interface demonstrated via an ArrayList object.

gr/aueb/cs/collections/IndexTraversalError.java → gr/aueb/cs/examples/collections/IndexTraversalError.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.collections;
+package gr.aueb.cs.examples.collections;
 
 import java.util.*;
 

gr/aueb/cs/collections/IteratorTraversalSafe.java → gr/aueb/cs/examples/collections/IteratorTraversalSafe.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.collections;
+package gr.aueb.cs.examples.collections;
 
 import java.util.ArrayList;
 import java.util.Iterator;

gr/aueb/cs/collections/ListTest.java → gr/aueb/cs/examples/collections/ListTest.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.collections;
+package gr.aueb.cs.examples.collections;
 // Working on the example of Deitel (pp 837, 9th edition)
 // re. Lists, LinkedLists and ListIterators.
 

gr/aueb/cs/collections/PriorityQueueTest.java → gr/aueb/cs/examples/collections/PriorityQueueTest.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.collections;
+package gr.aueb.cs.examples.collections;
 
 import java.util.Comparator;
 import java.util.PriorityQueue;

gr/aueb/cs/exceptions/DivideByZeroSafely.java → gr/aueb/cs/examples/exceptions/DivideByZeroSafely.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.exceptions;
+package gr.aueb.cs.examples.exceptions;
 
 import java.util.InputMismatchException;
 

gr/aueb/cs/exceptions/DivideByZeroWithoutExceptionHandling.java → gr/aueb/cs/examples/exceptions/DivideByZeroWithoutExceptionHandling.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.exceptions;
+package gr.aueb.cs.examples.exceptions;
 
 import java.util.Scanner;
 

gr/aueb/cs/examples/exceptions/ThrowTest.java

@@ -0,0 +1,11 @@
+package gr.aueb.cs.examples.exceptions;
+
+public class ThrowTest {
+    public static void main(String[] args) {
+        try {
+            throw new RuntimeException("Σφάλμα!");
+        } catch (RuntimeException e) {
+            System.out.println("Πιάστηκε εξαίρεση: " + e.getMessage());
+        }
+    }
+}

gr/aueb/cs/files/GreekReaderUTF8.java → gr/aueb/cs/examples/files/GreekReaderUTF8.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.files;
+package gr.aueb.cs.examples.files;
 
 import java.io.*;
 
@@ -8,7 +8,7 @@ public static void main(String[] args) throws IOException {
         // δεν είναι ασφαλές για UTF-8.
         BufferedReader reader = new BufferedReader(
                 new InputStreamReader(
-                        new FileInputStream("greek.txt"), "UTF-8" // δοκιμάστε "ISO-8859-7" για πείραμα
+                        new FileInputStream("gr/aueb/cs/examples/files/greek.txt"), "UTF-8" // δοκιμάστε "ISO-8859-7" για πείραμα
                 )
         );
 
@@ -19,4 +19,4 @@ public static void main(String[] args) throws IOException {
 
         reader.close();
     }
-}
+}

gr/aueb/cs/files/GreekWriterUTF8.java → gr/aueb/cs/examples/files/GreekWriterUTF8.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.files;
+package gr.aueb.cs.examples.files;
 
 import java.io.*;
 
@@ -7,7 +7,7 @@ public static void main(String[] args) throws IOException {
         // Δημιουργία Writer με ρητή κωδικοποίηση UTF-8
         BufferedWriter writer = new BufferedWriter(
                 new OutputStreamWriter(
-                        new FileOutputStream("greek.txt"), "UTF-8"
+                        new FileOutputStream("gr/aueb/cs/examples/files/greek.txt"), "UTF-8"
                 )
         );
 
@@ -18,6 +18,6 @@ public static void main(String[] args) throws IOException {
         writer.write("Αυτό είναι δοκιμαστικό αρχείο σε UTF-8.");
         writer.close();
 
-        System.out.println("Το αρχείο greek.txt γράφτηκε με επιτυχία σε UTF-8.");
+        System.out.println("Το αρχείο gr/aueb/cs/examples/files/greek.txt γράφτηκε με επιτυχία σε UTF-8.");
     }
 }

gr/aueb/cs/files/LibraryReader.java → gr/aueb/cs/examples/files/LibraryReader.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.files;
+package gr.aueb.cs.examples.files;
 
 import org.w3c.dom.*;
 import javax.xml.parsers.*;
@@ -7,7 +7,7 @@
 public class LibraryReader {
     public static void main(String[] args) throws Exception {
         // Βήμα 1: Φόρτωση και parsing του XML
-        File xmlFile = new File("library.xml");
+        File xmlFile = new File("gr/aueb/cs/examples/files/library.xml");
         DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
         DocumentBuilder builder = factory.newDocumentBuilder();
         Document doc = builder.parse(xmlFile);

gr/aueb/cs/files/RepresentationsTest.java → gr/aueb/cs/examples/files/RepresentationsTest.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.files;
+package gr.aueb.cs.examples.files;
 
 public class RepresentationsTest {
 

gr/aueb/cs/files/URLReader.java → gr/aueb/cs/examples/files/URLReader.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.files;
+package gr.aueb.cs.examples.files;
 
 import java.net.URL;
 import java.io.BufferedReader;

gr/aueb/cs/examples/files/greek.txt

@@ -0,0 +1,3 @@
+Καλημέρα
+Πώς είσαι;
+Αυτό είναι δοκιμαστικό αρχείο σε UTF-8.

gr/aueb/cs/examples/files/library.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<library>
+    <section name="Programming">
+        <book title="Effective Java" author="Joshua Bloch" year="2018" />
+        <book title="Clean Code" author="Robert C. Martin" year="2008" />
+    </section>
+    <section name="Computer Science">
+        <book title="Introduction to Algorithms" author="Cormen, Leiserson, Rivest, Stein" year="2022" />
+    </section>
+</library>

gr/aueb/cs/generics/BoundedTypeParamsTest.java → gr/aueb/cs/examples/generics/BoundedTypeParamsTest.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.generics;
+package gr.aueb.cs.examples.generics;
 
 public class BoundedTypeParamsTest {
     public static void main(String[] args) {

gr/aueb/cs/generics/GenericMethodTest.java → gr/aueb/cs/examples/generics/GenericMethodTest.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.generics;
+package gr.aueb.cs.examples.generics;
 
 public class GenericMethodTest {
     public static void main(String[] args) {

gr/aueb/cs/generics/GenericsTest.java → gr/aueb/cs/examples/generics/GenericsTest.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.generics;
+package gr.aueb.cs.examples.generics;
 
 import java.util.ArrayList;
 

gr/aueb/cs/generics/StudentSortingComparatorDemo.java → gr/aueb/cs/examples/generics/StudentSortingComparatorDemo.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.generics;
+package gr.aueb.cs.examples.generics;
 
 import java.util.*;
 

gr/aueb/cs/generics/TypeErasureTest.java → gr/aueb/cs/examples/generics/TypeErasureTest.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.generics;
+package gr.aueb.cs.examples.generics;
 
 import java.util.ArrayList;
 import java.util.List;

gr/aueb/cs/graphics/JavaTagCloud.java → gr/aueb/cs/examples/graphics/JavaTagCloud.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.graphics;
+package gr.aueb.cs.examples.graphics;
 
 import java.awt.*;
 import java.awt.geom.AffineTransform;

gr/aueb/cs/inheritance/DynamicBinding.java → gr/aueb/cs/examples/inheritance/DynamicBinding.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.inheritance;
+package gr.aueb.cs.examples.inheritance;
 
 class Sup {
     void who() { System.out.println("who() in Sup"); }

gr/aueb/cs/inheritance/Final.java → gr/aueb/cs/examples/inheritance/Final.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.inheritance;
+package gr.aueb.cs.examples.inheritance;
 
 public class Final {
     public static void main(String[] args) {

gr/aueb/cs/inheritance/Polymorphism.java → gr/aueb/cs/examples/inheritance/Polymorphism.java

@@ -1,4 +1,4 @@
-package gr.aueb.cs.inheritance;
+package gr.aueb.cs.examples.inheritance;
 
 class X {
     int a;