本文共 2120 字，大约阅读时间需要 7 分钟。

一、概述

       装饰模式（Decorator），动态的给一个对象添加额外的职责，就增加功能来说，装饰模式比生成子类更为灵活。 

二、UML图示

三、编程实现

       该程序主要通过模拟饮料配料的功能实现。

1、饮品抽象类，其他类都继承该类。

public abstract class Drink {    public String name;    public String getDescription(){        return name;    }    public abstract double cost();}

2、饮品实现类

      2.1 咖啡

public class Coffee extends Drink {    public Coffee(){        name = "咖啡";    }    @Override    public double cost() {        return 15;    }}

2.2 茶

public class Tea extends Drink {    public Tea(){        name = "茶";    }    @Override    public double cost() {        return 20;    }}

3、配料抽象类

public abstract class ExtraAddings extends Drink{    public abstract String getDescription();}

4、配料实现类

4.1 加奶

public class Milk extends ExtraAddings {    Drink drink;    public Milk(Drink drink){        this.drink = drink;    }    @Override    public String getDescription() {        return drink.getDescription()+"+牛奶";    }    public double cost(){        return 3+drink.cost();    }}

4.2 加糖

public class Sugar extends ExtraAddings {    Drink drink;    public Sugar(Drink drink){        this.drink = drink;    }    @Override    public String getDescription() {        return drink.getDescription() + "+糖";    }    public double cost(){        return 2 + drink.cost();    }}

5、测试类

public class Test {    public static void main(String[] args) {        Drink drink1 = new Coffee();        Drink drink2 = new Tea();        Drink addMilk = new Milk(drink1);        Drink addSugar = new Sugar(drink1);        Drink addMilk2 = new Milk(drink2);        Drink addSugar2 = new Sugar(drink2);        Drink addAll1 = new Milk(addSugar);        Drink addAll2 = new Sugar(addMilk2);        System.out.println(addMilk.getDescription()+addMilk.cost());        System.out.println(addSugar.getDescription()+addSugar.cost());        System.out.println(addMilk2.getDescription()+addMilk2.cost());        System.out.println(addSugar2.getDescription()+addSugar2.cost());        System.out.println(addAll1.getDescription()+addAll1.cost());        System.out.println(addAll2.getDescription()+addAll2.cost());    }}结果：咖啡+牛奶18.0咖啡+糖17.0茶+牛奶23.0茶+糖22.0咖啡+糖+牛奶20.0茶+牛奶+糖25.0