what is delegation in java with code examples

import java.util.EventObject;
import java.util.EventListener;

class MyEvent extends EventObject {
    public MyEvent(Object source) {
        super(source);
    }
}

interface MyEventListener extends EventListener {
    public void handleEvent(MyEvent event);
}

class MyButton {
    private MyEventListener listener;

    public void addEventListener(MyEventListener l) {
        listener = l;
    }

    public void click() {
        if (listener != null) {
            listener.handleEvent(new MyEvent(this));
        }
    }
}

class MyFrame {
    public MyFrame() {
        MyButton button = new MyButton();
        button.addEventListener(new MyEventListener() {
            public void handleEvent(MyEvent event) {
                System.out.println("Button clicked!");
            }
        });
    }
}

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

interface MyInterface {
    public void doSomething();
}

class MyDelegate implements MyInterface {
    public void doSomething() {
        System.out.println("MyDelegate.doSomething() called");
    }
}

class MyInvocationHandler implements InvocationHandler {
    private MyInterface delegate;

    public MyInvocationHandler(MyInterface delegate) {
        this.delegate = delegate;
    }

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("MyInvocationHandler.invoke() called for method " + method.getName());
        return method.invoke(delegate,
Delegation in Java can also be used in conjunction with other design patterns, such as the Decorator pattern. The Decorator pattern allows for the dynamic addition of new behavior to an object without changing its class. This can be achieved by using delegation to forward method calls to a decorated object, while adding additional behavior before or after the call.

Another design pattern that often uses delegation is the Strategy pattern. The Strategy pattern is used to encapsulate different algorithms or behaviors and make them interchangeable. In this context, the delegate is the strategy object and the delegator is the context object that forwards method calls to the appropriate strategy.

Delegation can also be used in conjunction with the Template Method pattern, which defines the skeleton of an algorithm in a base class and allows subclasses to fill in the details. In this case, the base class would use delegation to call a method that is implemented by the subclass.

It's also worth mentioning that, delegation can be implemented using different techniques like inheritance, composition, and interfaces. In Inheritance, a subclass can inherit the behavior of its superclass and add or override its own behavior. In composition, an object has an instance of another object and forward method calls to it. And in interfaces, an object implements an interface and delegate method calls to an instance of a class that also implements that interface.

In conclusion, delegation is a powerful design pattern that allows for a clear separation of responsibilities between objects and can make code more modular and easier to maintain. It can be used in conjunction with other design patterns, such as the Decorator, Strategy, and Template Method patterns, and can be implemented using different techniques like inheritance, composition, and interfaces.

## Popular questions 
1. What is delegation in Java? 
- Delegation in Java is a design pattern that allows one object (the delegate) to handle a request made to another object (the delegator). The delegator is responsible for forwarding the request to the delegate, and the delegate is responsible for handling the request.

2. What is the purpose of using delegation in Java?
- The purpose of using delegation in Java is to achieve a clear separation of responsibilities between objects and make code more modular and easier to maintain.

3. Can you give an example of how delegation might be used in Java?
- One common example of delegation in Java is the use of the `java.util.EventObject` and `java.util.EventListener` classes. The `EventObject` class can be used to represent an event, such as a button click or a key press, and the `EventListener` interface can be implemented by any class that wants to handle events.

4. Are there any other design patterns that can be used in conjunction with delegation?
- Yes, other design patterns that can be used in conjunction with delegation include the Decorator, Strategy, and Template Method patterns.

5. How can delegation be implemented in Java?
- Delegation can be implemented in Java using different techniques such as inheritance, composition, and interfaces. In Inheritance, a subclass can inherit the behavior of its superclass and add or override its own behavior. In composition, an object has an instance of another object and forward method calls to it. And in interfaces, an object implements an interface and delegate method calls to an instance of a class that also implements that interface.

### Tag 
Delegation