外观模式-Facade
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外观模式是为了解决类与类之间依赖关系的,外观模式将类间关系放在一个Facade类中,降低了类类之间的耦合度,该模式中不涉及接口
举一个经典的例子:
CPU类:
1 public class CPU { 2 public void startup(){ 3 System.out.println("cpu startup"); 4 } 5 6 public void shutdown(){ 7 System.out.println("cpu shutdown"); 8 } 9 }
Mainboard类:
1 public class Mainboard { 2 3 public void startup(){ 4 System.out.println("mainboard startup"); 5 } 6 7 public void shutdown(){ 8 System.out.println("mainboard shutdown"); 9 } 10 }
Disk类:
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 }
Computer类(外观类):
1 public class Computer { 2 private CPU cpu; 3 private Mainboard mainboard; 4 private Disk disk; 5 6 public Computer(){ 7 cpu = new CPU(); 8 mainboard = new Mainboard(); 9 disk = new Disk(); 10 } 11 12 public void startup(){ 13 System.out.println("starting the computer"); 14 cpu.startup(); 15 mainboard.startup(); 16 disk.startup(); 17 System.out.println("computer is started"); 18 } 19 20 public void shutdown(){ 21 System.out.println("closing the computer"); 22 disk.shutdown(); 23 mainboard.shutdown(); 24 cpu.shutdown(); 25 System.out.println("computer is closed"); 26 } 27 }
测试类:
1 public class Main { 2 3 public static void main(String[] args) { 4 Computer computer = new Computer(); 5 computer.startup(); 6 computer.shutdown(); 7 } 8 }
测试结果:
starting the computer cpu startup mainboard startup disk startup computer is started closing the computer disk shutdown mainboard shutdown cpu shutdown computer is closed
如果我们没有外观类(Computer),CPU、Mainboard、Disk之间将会相互持有实例对象,造成严重的依赖;而有了Computer,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!
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