外觀模式(Facade)
外觀模式是爲了解決類與類之家的依賴關係的,像spring一樣,可以將類和類之間的關係配置到配置文件中,而外觀模式就是將他們的關係放在一個Facade類中,降低了類類之間的耦合度,該模式中沒有涉及到接口。
看下類圖:(我們以一個計算機的啓動過程爲例)
我們先看下實現類:
public class CPU {
public void startup(){
System.out.println("cpu startup!");
}
public void shutdown(){
System.out.println("cpu shutdown!");
}
}
public class Memory {
public void startup(){
System.out.println("memory startup!");
}
public void shutdown(){
System.out.println("memory shutdown!");
}
}
public class Disk {
public void startup(){
System.out.println("disk startup!");
}
public void shutdown(){
System.out.println("disk shutdown!");
}
}
public class Computer {
private CPU cpu;
private Memory memory;
private Disk disk;
public Computer(){
cpu = new CPU();
memory = new Memory();
disk = new Disk();
}
public void startup(){
System.out.println("start the computer!");
cpu.startup();
memory.startup();
disk.startup();
System.out.println("start computer finished!");
}
public void shutdown(){
System.out.println("begin to close the computer!");
cpu.shutdown();
memory.shutdown();
disk.shutdown();
System.out.println("computer closed!");
}
}
User類如下:
public class User {
public static void main(String[] args) {
Computer computer = new Computer();
computer.startup();
computer.shutdown();
}
}
輸出:
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!
如果我們沒有Computer類,那麼,CPU、Memory、Disk他們之間將會相互持有實例,產生關係,這樣會造成嚴重的依賴,修改一個類,可能會帶來其他類的修改,這不是我們想要看到的,有了Computer類,他們之間的關係被放在了Computer類裏,這樣就起到了解耦的作用,這,就是外觀模式!