设计模式（八） ： 结构型模式－－装饰模式

装饰模式的目的是为了给一个对象动态的增加一些功能。装饰对象和被装饰的对象实现同一个接口，装饰对象持有被装饰对象的实例。

类图：

示意性代码：

package com.javadesignpattern.Decorator;



public interface Component {

    

    void sampleOperation();



}

package com.javadesignpattern.Decorator;



public class ConcreteComponent implements Component{



    public void sampleOperation() {

        // TODO Auto-generated method stub

        System.out.println(ConcreteComponent.class + ": sampleOperation function");

    }

}

package com.javadesignpattern.Decorator;



public class Decorator implements Component{

    

    Component component;

    

    public Decorator(Component component){

        this.component = component;

    }

    



    public void sampleOperation() {

        // TODO Auto-generated method stub

        component.sampleOperation();

        System.out.println(Decorator.class + " : sampleOperation function");

    }



}

package com.javadesignpattern.Decorator;



public class ConcreteDecorator extends Decorator{

    Decorator dec;

    

    public ConcreteDecorator(Decorator dec){

        super(dec.component);

        this.dec = dec;

    }

    

    public void sampleOperation(){

        super.sampleOperation();

        System.out.println(ConcreteDecorator.class + " : sampleOperation function");

    }



}

package com.javadesignpattern.Decorator;



public class Client {

    

    public static void main(String[] ags){

        Component componemt = new Decorator(new ConcreteComponent());

        componemt.sampleOperation();        

        System.out.println("--------------------");

        

        Component componemt1 = new ConcreteDecorator(new Decorator(new ConcreteComponent()));

        componemt1.sampleOperation();

        System.out.println("--------------------");

    }



}

装饰模式以这样的形式出现：

new Decorator1(new Decorator2(new Decorator3(new ConcreteComponent())))

装饰模式在什么场景下使用：

1. 需要扩展一个类的功能

2. 动态的给一个对象增加一些功能

3. 需要一些扩展类的功能，但是有很多类，这样使得继承变得不太现实。