设计模式-装饰器（Decorator）模式

主要角色

• 实体类
• 装饰者

职责

动态的给类加模块

类图

代码

public abstract class ABattercake {
    protected abstract String getDesc();
    protected abstract int cost();
}
---
public abstract class AbstractDecorator extends ABattercake {
    private ABattercake aBattercake;

    public AbstractDecorator(ABattercake aBattercake) {
        this.aBattercake = aBattercake;
    }

    protected abstract void doSomething();

    @Override
    protected String getDesc() {
        return this.aBattercake.getDesc();
    }

    @Override
    protected int cost() {
        return this.aBattercake.cost();
    }
}
---
public class Battercake extends ABattercake {
    @Override
    protected String getDesc() {
        return "煎饼";
    }

    @Override
    protected int cost() {
        return 8;
    }
}
---
public class EggDecorator extends AbstractDecorator {
    public EggDecorator(ABattercake aBattercake) {
        super(aBattercake);
    }

    @Override
    protected void doSomething() {

    }

    @Override
    protected String getDesc() {
        return super.getDesc()+" 加一个鸡蛋";
    }

    @Override
    protected int cost() {
        return super.cost()+1;
    }
}
---
public class SausageDecorator extends AbstractDecorator{
    public SausageDecorator(ABattercake aBattercake) {
        super(aBattercake);
    }

    @Override
    protected void doSomething() {

    }

    @Override
    protected String getDesc() {
        return super.getDesc()+" 加一根香肠";
    }

    @Override
    protected int cost() {
        return super.cost()+2;
    }
}

使用

public class Test {
    public static void main(String[] args) {
        ABattercake aBattercake;
        aBattercake = new Battercake();
        aBattercake = new EggDecorator(aBattercake);
        aBattercake = new EggDecorator(aBattercake);
        aBattercake = new SausageDecorator(aBattercake);

        System.out.println(aBattercake.getDesc()+" 销售价格:"+aBattercake.cost());
    }
}

技巧

• 装饰器的作用就像是给一张相片装不同的相框一样。