门面模式

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类图

代码

SubSystem

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class Cpu{
    void start(){
        System.out.println("CPU启动");
    }
}

class Memory{
    void start(){
        System.out.println("内存启动");
    }
}

System

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class Computer{
    private Cpu cpu;

    private Memory memory;

    public Cpu getCpu() {
        return cpu;
    }

    public void setCpu(Cpu cpu) {
        this.cpu = cpu;
    }

    public Memory getMemory() {
        return memory;
    }

    public void setMemory(Memory memory) {
        this.memory = memory;
    }

    public void start(){
        cpu.start();
        memory.start();
    }
}

测试类

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public class Main {
    public static void main(String args[]){
        Cpu cpu = new Cpu();
        Memory memory = new Memory();
        Computer computer = new Computer();
        computer.setCpu(cpu);
        computer.setMemory(memory);
        computer.start();
    }
}

总结

优点

  1. 实现子系统与客户之间的解耦
  2. 提供统一入口简化客户端调用

缺点

如果子类变更过多，会导致入口处也会有变化，违反了开闭原则