Project 1

project_1/adapter_design_pattern/Main.java

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+class Motor {
+	public void spin(){
+		System.out.println("the rotor is spinning");
+	}
+}
+
+class Wheel {
+	public void moveCar(){
+		System.out.println("the wheel moves the car in a certain direction");
+	}
+}
+
+class TransmissionBeltAdapter extends Wheel {
+	Motor motor;
+	public TransmissionBeltAdapter(Motor motor){
+		// reference to the object we are adapting (i.e. the motor)
+		this.motor = motor;
+	}
+
+	public void moveCar () {
+		motor.spin();
+	}
+}
+
+class Main
+{
+    public static void main(String args[])
+    {
+        Motor motor = new Motor();
+        Wheel wheel = new Wheel();
+
+        Wheel transmissionBeltAdapter = new TransmissionBeltAdapter(motor);
+
+        motor.spin();
+        wheel.moveCar();
+  		// the adapter will do the same thing as the motor, it will spin the wheel
+  		System.out.println("The transmission belt will transfer the energy of the motor to the wheel while");
+        transmissionBeltAdapter.moveCar();
+    }
+}

project_1/singleton_design_pattern/SocketClass.java

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+package singleton_design_pattern;
+import java.io.Serializable;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.io.IOException;
+import java.io.ObjectOutput;
+import java.io.ObjectInput;
+
+public class SocketClass implements Serializable {
+
+    private static volatile SocketClass sSoleInstance;
+
+    //private constructor.
+    private SocketClass(){
+
+        //Prevent from the reflection api.
+        if (sSoleInstance != null){
+            throw new RuntimeException("Use getInstance() method to get the single instance of this class.");
+        }
+    }
+
+    public static SocketClass getInstance() {
+        if (sSoleInstance == null) { //if there is no instance available create one
+            synchronized (SocketClass.class) {
+                if (sSoleInstance == null) sSoleInstance = new SocketClass();
+            }
+        }
+
+        return sSoleInstance;
+    }
+
+    //Make singleton from serialize and deserialize operation.
+    protected SocketClass readResolve() {
+        return getInstance();
+    }
+}

project_1/singleton_design_pattern/SocketTester.java

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+package singleton_design_pattern;
+import java.io.Serializable;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.io.IOException;
+import java.io.ObjectOutput;
+import java.io.ObjectInput;
+
+
+public class SocketTester {
+   public static void main(String[] args) {
+
+      try {
+            SocketClass instance1 = SocketClass.getInstance();
+            ObjectOutput out = null;
+
+            out = new ObjectOutputStream(new FileOutputStream("filename.ser"));
+            out.writeObject(instance1);
+            out.close();
+
+            //deserialize from file to object
+            ObjectInput in = new ObjectInputStream(new FileInputStream("filename.ser"));
+            SocketClass instance2 = (SocketClass) in.readObject();
+            in.close();
+
+            //makes sure the object was not instantiated twice from deserialization
+            instance2 = instance2.readResolve(); 
+
+            System.out.println("instance1 hashCode=" + instance1.hashCode());
+            System.out.println("instance2 hashCode=" + instance2.hashCode());
+
+        } catch (IOException | ClassNotFoundException e) {
+            e.printStackTrace();
+        }
+   }
+}