设计模式——外观模式

说明

外观模式是为了解决类与类之家的依赖关系的，像spring一样，可以将类和类之间的关系配置到配置文件中，而外观模式就是将他们的关系放在一个Facade类中，降低了类类之间的耦合度，该模式中没有涉及到接口，看下类图：（我们以一个计算机的启动过程为例）

示例

下面看下外观模式的代码实现

class CPU{
    public function startup(){
        echo "cpu startup!" . PHP_EOL;
    }

    public function shutdown(){
        echo "cpu shutdown!" . PHP_EOL;
    }
}

class Memory{
    public function startup(){
        echo "memory startup!" . PHP_EOL;
    }

    public function shutdown(){
        echo "memory shutdown!" . PHP_EOL;
    }
}

class Disk{
    public function startup(){
        echo "disk startup!" . PHP_EOL;
    }

    public function shutdown(){
        echo "disk shutdown!" . PHP_EOL;
    }
}

class Computer{
    private CPU $cpu;
    private Memory $memory;
    private Disk $disk;

    public function __construct(){
        $this->cpu = new CPU();
        $this->memory = new Memory();
        $this->disk = new Disk();
    }

    public function startup(){
        echo "start the computer!" . PHP_EOL;
        $this->cpu->startup();
        $this->memory->startup();
        $this->disk->startup();
        echo "start computer finished!" . PHP_EOL;
    }

    public function shutdown(){
        echo "begin to close th computer!" . PHP_EOL;
        $this->cpu->shutdown();
        $this->memory->shutdown();
        $this->disk->shutdown();
        echo "computer closed!" . PHP_EOL;
    }
}


//调用
$computer = new Computer();
$computer->startup();
$computer->shutdown();

/**
 * output:
 *
start the computer!
cpu startup!
memory startup!
disk startup!
start computer finished!
begin to close th computer!
cpu shutdown!
memory shutdown!
disk shutdown!
computer closed!

class CPU{
    public function startup(){
        echo "cpu startup!" . PHP_EOL;
    }

    public function shutdown(){
        echo "cpu shutdown!" . PHP_EOL;
    }
}

class Memory{
    public function startup(){
        echo "memory startup!" . PHP_EOL;
    }

    public function shutdown(){
        echo "memory shutdown!" . PHP_EOL;
    }
}

class Disk{
    public function startup(){
        echo "disk startup!" . PHP_EOL;
    }

    public function shutdown(){
        echo "disk shutdown!" . PHP_EOL;
    }
}

class Computer{
    private CPU $cpu;
    private Memory $memory;
    private Disk $disk;

    public function __construct(){
        $this->cpu = new CPU();
        $this->memory = new Memory();
        $this->disk = new Disk();
    }

    public function startup(){
        echo "start the computer!" . PHP_EOL;
        $this->cpu->startup();
        $this->memory->startup();
        $this->disk->startup();
        echo "start computer finished!" . PHP_EOL;
    }

    public function shutdown(){
        echo "begin to close th computer!" . PHP_EOL;
        $this->cpu->shutdown();
        $this->memory->shutdown();
        $this->disk->shutdown();
        echo "computer closed!" . PHP_EOL;
    }
}


//调用
$computer = new Computer();
$computer->startup();
$computer->shutdown();

/**
 * output:
 *
start the computer!
cpu startup!
memory startup!
disk startup!
start computer finished!
begin to close th computer!
cpu shutdown!
memory shutdown!
disk shutdown!
computer closed!

 */

总结

如果我们没有Computer类，那么，CPU、Memory、Disk他们之间将会相互持有实例，产生关系，这样会造成严重的依赖，修改一个类，可能会带来其他类的修改，这不是我们想要看到的，有了Computer类，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！