Solution

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

@@ -0,0 +1,13 @@
+package core.basesyntax;
+
+public class Bulldozer extends Machine {
+    @Override
+    public void doWork() {
+        System.out.println("Bulldozer started work.");
+    }
+
+    @Override
+    public void stopWork() {
+        System.out.println("Bulldozer stopped work.");
+    }
+}

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

@@ -0,0 +1,13 @@
+package core.basesyntax;
+
+public class Excavator extends Machine {
+    @Override
+    public void doWork() {
+        System.out.println("Excavator started work.");
+    }
+
+    @Override
+    public void stopWork() {
+        System.out.println("Excavator stopped work.");
+    }
+}

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

@@ -0,0 +1,7 @@
+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[] machines = {
+                new Truck(),
+                new Bulldozer(),
+                new Excavator()
+        };
+        for (Machine machine : machines) {
+            machine.doWork();
+            machine.stopWork();
+        }
+    }
 
 }

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

@@ -0,0 +1,13 @@
+package core.basesyntax;
+
+public class Truck extends Machine {
+    @Override
+    public void doWork() {
+        System.out.println("Truck started work.");
+    }
+
+    @Override
+    public void stopWork() {
+        System.out.println("Truck stopped work.");
+    }
+}