外观模式

UML
Java
Racket/Common-Lisp

外观模式是为了解决类与类之间的依赖关系的，将他们的关系放在一个Facade类中，降低了类与类之间的耦合度

UML

Java

编写CPU, Memory, Disk类

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!");
    }
}

编写Computer类来简化客户端调用：

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!");
    }
}

测试类：

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

测试结果：

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!

Racket/Common-Lisp

函数式编程往往使用module或者package来模块化代码：

通过宏把函数编译到module或者package中
客户端通过import module/require package来进行调用

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外观模式

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UML

Java

Racket/Common-Lisp