Solution

src/main/java/core/basesyntax/Bulldozer.java

@@ -0,0 +1,11 @@
+package core.basesyntax;
+
+public class Bulldozer extends Machine {
+    public void doWork() {
+        System.out.println("Bulldozer started its work");
+    }
+
+    public void stopWork() {
+        System.out.println("Bulldozer stopped working");
+    }
+}

src/main/java/core/basesyntax/Excavator.java

@@ -0,0 +1,11 @@
+package core.basesyntax;
+
+public class Excavator extends Machine {
+    public void doWork() {
+        System.out.println("Excavator started its work");
+    }
+
+    public void stopWork() {
+        System.out.println("Excavator stopped working");
+    }
+}

src/main/java/core/basesyntax/Machine.java

@@ -0,0 +1,8 @@
+package core.basesyntax;
+
+public abstract class Machine {
+    public abstract void doWork();
+
+    public abstract void stopWork();
+}
+

src/main/java/core/basesyntax/MainApp.java

@@ -1,5 +1,17 @@
 package core.basesyntax;
 
 public class MainApp {
+    public static void main(String[] args) {
+        Machine truc = new Truck();
+        truc.doWork();
+        truc.stopWork();
 
+        Machine bulldozer = new Bulldozer();
+        bulldozer.doWork();
+        bulldozer.stopWork();
+
+        Machine excavator = new Excavator();
+        excavator.doWork();
+        excavator.stopWork();
+    }
 }

src/main/java/core/basesyntax/Truck.java

@@ -0,0 +1,11 @@
+package core.basesyntax;
+
+public class Truck extends Machine {
+    public void doWork() {
+        System.out.println("Truck started its work");
+    }
+
+    public void stopWork() {
+        System.out.println("Truck stopped working");
+    }
+}