Fixed issues

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 its work.");
+    }
+
+    public void stopWork() {
+        System.out.println("Bulldozer has stopped working.");
+    }
+}
+

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 its work.");
+    }
+
+    public void stopWork() {
+        System.out.println("Excavator has stopped working.");
+    }
+}
+

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 its work.");
+    }
+
+    public void stopWork() {
+        System.out.println("Truck has stopped working.");
+    }
+}
+