使用场景

外观模式：将内部系统和外部系统隔离，不直接访问；从中间加入一个门店，所有外面访问门店，然后门店访问内部系统。以电脑为例，内存、CPU、硬盘都是内部系统，而这个门店就是电脑了，我们用户就是直接操作电脑操作系统来操作那些。

代码例子

内存、CPU、硬盘

public class Memory {
public void startup() {
System.out.println("memory startup!");
}
public void shutdown() {
System.out.println("memory shutdown!");
}
}
public class CPU {
public void startup() {
System.out.println("cpu startup!");
}
public void shutdown() {
System.out.println("cpu shutdown!");
}
}
public class Disk {
public void startup() {
System.out.println("disk startup!");
}
public void shutdown() {
System.out.println("disk shutdown!");
}
}

电脑

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!");
}
}

main函数

public class Test {
public static void main(String[] args) {
Computer computer = new Computer();
computer.startup();
computer.shutdown();
}
}