1.定义

装饰者模式(Decorator Pattern) 是指在不改变原有对象的基础之上
将功能附加到对象上,提供了比继承更有弹性的替代方案
属于机构型模式

2.适用场景

1.扩展类的功能或者为其附加新的职责
2.动态的给一个对象添加功能,这些功能可以动态的撤销

3.代码

传统继承

image.png

/**
 * Description:煎饼
 *
 * @date 2019-05-28 16:43
 */

public class Pancake {

    public String getName(){
        return "煎饼";
    }

    public BigDecimal getPrice(){
        return BigDecimal.TEN;
    }

}

/**
 * Description:鸡蛋煎饼
 *
 * @date 2019-05-28 16:43
 */

public class EggPancake extends Pancake{

    public String getName(){
        return "鸡蛋"+super.getName();
    }

    public BigDecimal getPrice(){
        return super.getPrice().add(BigDecimal.valueOf(5L));
    }

}

 * Description:香肠鸡蛋煎饼
 *
 * @date 2019-05-28 16:43
 */

public class SausageEggPancake extends EggPancake{

    public String getName(){
        return "香肠"+super.getName();
    }

    public BigDecimal getPrice(){
        return super.getPrice().add(BigDecimal.valueOf(5L));
    }

}

/**
 * Description:测试类
 *
 * @date 2019-05-28 16:54
 */

public class Test {

    public static void main(String[] args) {
        Pancake pancake = new Pancake();
        System.out.println(pancake.getName()+",价格:"+pancake.getPrice());

        Pancake eggPancake = new EggPancake();
        System.out.println(eggPancake.getName()+",价格:"+eggPancake.getPrice());

        Pancake sausageEggPancake = new SausageEggPancake();
        System.out.println(sausageEggPancake.getName()+",价格:"+sausageEggPancake.getPrice());
    }

}

装饰者模式

image.png

/**
 * Description:煎饼
 *
 * @date 2019-05-28 16:43
 */

public abstract class Pancake {

    public abstract String getName();

    public abstract BigDecimal getPrice();

}

/**
 * Description:普通煎饼
 *
 * @date 2019-05-28 16:43
 */

public  class BasePancake extends Pancake{

    @Override
    public  String getName(){
        return "煎饼";
    }
    @Override
    public  BigDecimal getPrice(){
        return BigDecimal.TEN;
    }

}

/**
 * Description:煎饼装饰器
 *
 * @author zhangzhongbo
 * @date 2019-05-28 17:05
 */

public abstract class PancakeDecorator extends Pancake{

    private Pancake pancake;

    public PancakeDecorator(Pancake pancake) {
        this.pancake = pancake;
    }

    @Override
    public String getName() {
        return pancake.getName();
    }

    @Override
    public BigDecimal getPrice() {
        return pancake.getPrice();
    }
}

/**
 * Description:鸡蛋煎饼装饰器
 *
 * @date 2019-05-28 17:09
 */

public class EggPancakeDecorator extends PancakeDecorator {
    public EggPancakeDecorator(Pancake pancake) {
        super(pancake);
    }

    @Override
    public String getName() {
        return "鸡蛋"+super.getName();
    }

    @Override
    public BigDecimal getPrice() {
        return super.getPrice().add(BigDecimal.valueOf(5L));
    }
}

/**
 * Description:香肠煎饼装饰器
 *
 * @date 2019-05-28 17:09
 */

public class SausagePancakeDecorator extends PancakeDecorator {
    public SausagePancakeDecorator(Pancake pancake) {
        super(pancake);
    }

    @Override
    public String getName() {
        return "香肠"+super.getName();
    }

    @Override
    public BigDecimal getPrice() {
        return super.getPrice().add(BigDecimal.valueOf(5L));
    }
}

和适配器模式的区别

image.png