结构型模式--外观模式（Facade）_JAVA_编程开发_程序员俱乐部

外观模式是为了解决类与类之家的依赖关系的，像spring一样，可以将类和类之间的关系配置到配置文件中，而外观模式就是将他们的关系放在一个Facade类中，降低了类类之间的耦合度，该模式中没有涉及到接口，看下类图：（我们以一个计算机的启动过程为例）

我们先看下实现类：

1. public?class?CPU?{??
2. ??????
3. ????public?void?startup(){??
4. ????????System.out.println("cpu?startup!");??
5. ????}??
6. ??????
7. ????public?void?shutdown(){??
8. ????????System.out.println("cpu?shutdown!");??
9. ????}??
10. }??

1. public?class?Memory?{??
2. ??????
3. ????public?void?startup(){??
4. ????????System.out.println("memory?startup!");??
5. ????}??
6. ??????
7. ????public?void?shutdown(){??
8. ????????System.out.println("memory?shutdown!");??
9. ????}??
10. }??

1. public?class?Disk?{??
2. ??????
3. ????public?void?startup(){??
4. ????????System.out.println("disk?startup!");??
5. ????}??
6. ??????
7. ????public?void?shutdown(){??
8. ????????System.out.println("disk?shutdown!");??
9. ????}??
10. }??

1. public?class?Computer?{??
2. ????private?CPU?cpu;??
3. ????private?Memory?memory;??
4. ????private?Disk?disk;??
5. ??????
6. ????public?Computer(){??
7. ????????cpu?=?new?CPU();??
8. ????????memory?=?new?Memory();??
9. ????????disk?=?new?Disk();??
10. ????}??
11. ??????
12. ????public?void?startup(){??
13. ????????System.out.println("start?the?computer!");??
14. ????????cpu.startup();??
15. ????????memory.startup();??
16. ????????disk.startup();??
17. ????????System.out.println("start?computer?finished!");??
18. ????}??
19. ??????
20. ????public?void?shutdown(){??
21. ????????System.out.println("begin?to?close?the?computer!");??
22. ????????cpu.shutdown();??
23. ????????memory.shutdown();??
24. ????????disk.shutdown();??
25. ????????System.out.println("computer?closed!");??
26. ????}??
27. }??

User类如下：

1. public?class?User?{??
2. ??
3. ????public?static?void?main(String[]?args)?{??
4. ????????Computer?computer?=?new?Computer();??
5. ????????computer.startup();??
6. ????????computer.shutdown();??
7. ????}??
8. }??

输出：

start the computer!
cpu startup!
memory startup!
disk startup!
start computer finished!
begin to close the computer!
cpu shutdown!
memory shutdown!
disk shutdown!
computer closed!

如果我们没有Computer类，那么，CPU、Memory、Disk他们之间将会相互持有实例，产生关系，这样会造成严重的依赖，修改一个类，可能会带来其他类的修改，这不是我们想要看到的，有了Computer类，他们之间的关系被放在了Computer类里，这样就起到了解耦的作用，这，就是外观模式！