JAVA设计模式之装饰模式

装饰模式：动态地将责任附加到对象上。若要扩展功能，装饰者提供了比继承更有弹性的替代方案。

例子：你要替一家咖啡店设计beverage类。beverage有很多种，并且可以添加许多的调料，比如蒸奶、豆浆、摩卡等。

 1 public abstract class Beverage
 2 {
 3     String description = "Unknown Beverage";
 4
 5     public String getDescription()
 6     {
 7         return description;
 8     }
 9
10     public abstract double cost();
11 }
12
13 public class Espresso extends Beverage
14 {
15     public Espresso()
16     {
17         description = "Espresso";
18     }
19
20     @Override
21     public double cost()
22     {
23         return 1.99;
24     }
25 }
26
27 public abstract class CondimentDecorator extends Beverage
28 {
29     public abstract String getDescription();
30 }
31
32 public class Mocha extends CondimentDecorator
33 {
34     Beverage beverage;
35
36     Mocha(Beverage beverage)
37     {
38         this.beverage = beverage;
39     }
40
41     @Override
42     public String getDescription()
43     {
44         return beverage.getDescription() + ", Mocha";
45     }
46
47     @Override
48     public double cost()
49     {
50         return .20 + beverage.cost();
51     }
52 }
53
54 public class Whip extends CondimentDecorator
55 {
56     Beverage beverage;
57
58     Whip(Beverage beverage)
59     {
60         this.beverage = beverage;
61     }
62
63     @Override
64     public String getDescription()
65     {
66         return beverage.getDescription() + ", Whip";
67     }
68
69     @Override
70     public double cost()
71     {
72         return .35 + beverage.cost();
73     }
74 }
75
76 public class test
77 {
78     public static void main(String[] args)
79     {
80         Beverage espresso = new Espresso();
81         Beverage espresso_mocha = new Mocha(espresso);
82         Beverage espresso_mocha_whip = new Whip(espresso_mocha);
83         output(espresso_mocha_whip);
84     }
85
86     public static void output(Beverage beverage)
87     {
88         System.out.println(beverage.getDescription() + " $: " + beverage.cost());
89     }
90 }

注：JAVA I/O中利用了装饰模式。