装饰者模式

来源：互联网发布：cisco 端口隔离编辑：程序博客网时间：2024/04/30 12:10

概念

动态地将责任附加到对象上

注意
* 装饰者和别装饰者继承自同一超类，且装饰者持有超类对象
* 继承的目的是继承类型，而不是行为
* 装饰者可以在别装饰者的行为前后加上新行为

例子
摘自《HEAD First 设计模式》,有少许改动
Mocha,Latte两种咖啡继承自Beverage，可以加入Milk，Soy两种调料，且可以重复加入。
Mocha，Latee 是被装饰者
“`java
public abstract class Beverage {
String description;
public abstract String getDescription();
public abstract double cost();
}

public class Mocha extends Beverage{
public Mocha()
{ description=”Mocha”;}
public double cost() {
return 1.5;
}

public String getDescription() {    return description;}

}

public class Latte extends Beverage {
Latte() {
description = “Latte”;
}
public double cost() {
return 2.5;
}
public String getDescription() {
return description;
}
}

` Milk,Soy是装饰者
public class Milk extends Beverage {

private Beverage beverage;public Milk(Beverage beverage) {    this.beverage = beverage;}public double cost() {    return beverage.cost()+0.5;}public String getDescription() {    return beverage.getDescription()+",Milk";}

}

public class Soy extends Beverage{
private Beverage beverage;

public  Soy( Beverage beverage) {    this.beverage=beverage;}public String getDescription() {    return beverage.getDescription()+",Soy";}public double cost() {    return beverage.cost()+0.5;}

}

测试代码

public class Test {
public static void main(String[] args) {
// TODO Auto-generated method stub
Beverage beverage1=new Mocha();
beverage1=new Milk(beverage1);
beverage1=new Milk(beverage1);
System.out.println(beverage1.getDescription()+” ￥”+beverage1.cost());

    Beverage beverage2=new Latte();    beverage2=new Soy(beverage2);    beverage2=new Milk(beverage2);    System.out.println(beverage2.getDescription()+" ￥"+beverage2.cost());        }

}
“`
测试结果

Mocha,Milk,Milk ￥2.5
Latte,Soy,Milk ￥3.5

0 0