Design Pattern Study Notes 2 - Adapter

Problem:
If want to reuse the existing class, but its interface does not meet the new requirement.

Solution:
Adapter pattern.

1) This is new interface we want to implement.
======================== Target.java ====================

package test.pattern.adapter;

public interface Target {

public void methodA();
public void methodB();
}

2) This is the existing class we have.
======================= Adaptee.java ================

package test.pattern.adapter;

public class Adaptee {

public void methodA() {
System.out.println("it is method A.");
}
}

3) This is an adapter class to implement above new interface Target.java

=================== Adapter.java =====================

package test.pattern.adapter;

public class Adapter extends Adaptee implements Target {

public void methodB() {

System.out.println("it is method B.");

}

}

4) This is another adapter to implement above new interface Target.java

=================== Adapter2.java ====================

package test.pattern.adapter;

public class Adapter2 implements Target {

private Adaptee adaptee;

public Adapter2(Adaptee adaptee) {

this.adaptee = adaptee;

}

public void methodA() {

this.adaptee.methodA();

}

public void methodB() {

System.out.println("this is method B.");

}

}

5) test class

============== Client.java ======================

package test.pattern.adapter;

public class Client {

public static void main(String[] args) {

Target adapter = new Adapter();

adapter.methodA();

adapter.methodB();

Adaptee adaptee = new Adaptee();

Target adapter2 = new Adapter2(adaptee);

adapter2.methodA();

adapter2.methodB();

}

}

This is output:

it is method A.

it is method B.

it is method A.

this is method B.