Created a Machine class that contains doWork and stopWork methods.

Created classes Truck, Bulldozer, Excavator that follow methods from Machine.
doWork prints that a certain machine has started its work.
stopWork prints that certain machines have stopped working.
In the MainApp class, a Machine array was created with the Truck, Bulldozer, Excavator methods that output messages from doWork and stopWork.

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

@@ -0,0 +1,14 @@
+package core.basesyntax;
+
+public class Bulldozer extends Machine {
+
+    @Override
+    public String goWork() {
+        return "Bulldozer started its work!";
+    }
+
+    @Override
+    public String stopWork() {
+        return "Bulldozer stopped its work!";
+    }
+}

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

@@ -0,0 +1,14 @@
+package core.basesyntax;
+
+public class Excavator extends Machine {
+
+    @Override
+    public String goWork() {
+        return "Excavator started its work!";
+    }
+
+    @Override
+    public String stopWork() {
+        return "Excavator stopped its work!";
+    }
+}

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

@@ -0,0 +1,8 @@
+package core.basesyntax;
+
+public abstract class Machine {
+
+    public abstract String goWork();
+
+    public abstract String 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 truck = new Truck();
+        Machine bulldozer = new Bulldozer();
+        Machine excavator = new Excavator();
+
+        String[] matrixMachine = {truck.goWork(),bulldozer.goWork(),excavator.goWork(),
+                truck.stopWork(), bulldozer.stopWork(), excavator.stopWork()};
+
+        for (String matrix : matrixMachine) {
+            System.out.println(matrix);
+        }
+    }
 }

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

@@ -0,0 +1,14 @@
+package core.basesyntax;
+
+public class Truck extends Machine {
+
+    @Override
+    public String goWork() {
+        return "Truck started its work!";
+    }
+
+    @Override
+    public String stopWork() {
+        return "Truck stopped its work!";
+    }
+}