php与设计模式-装饰器模式

装饰器模式

装饰器模式就是对一个已有的结构增加装饰。装饰模式是在不必改变原类文件和使用继承的情况下，动态地扩展一个对象的功能。它是通过创建一个包装对象，也就是装饰来包裹真实的对象。 基本说来, 如果想为现有对象增加新功能而不想影响其他对象, 就可以使用装饰器模式.

Demo：

abstract class Beverage{
    public $_name;
    abstract public function Cost();
}
// 被装饰者类
class Coffee extends Beverage{
    public function __construct(){
        $this->_name = 'Coffee';
    }  
    public function Cost(){
        return 1.00;
    }  
}
// 以下三个类是装饰者相关类
class CondimentDecorator extends Beverage{
    public function __construct(){
        $this->_name = 'Condiment';
    }  
    public function Cost(){
        return 0.1;
    }  
}
class Milk extends CondimentDecorator{
    public $_beverage;
    public function __construct($beverage){
        $this->_name = 'Milk';
        if($beverage instanceof Beverage){
            $this->_beverage = $beverage;
        }else
            exit('Failure');
    }  
    public function Cost(){
        return $this->_beverage->Cost() + 0.2;
    }  
}
class Sugar extends CondimentDecorator{
    public $_beverage;
    public function __construct($beverage){
        $this->_name = 'Sugar';
        if($beverage instanceof Beverage){
            $this->_beverage = $beverage;
        }else{
            exit('Failure');
        }
    }
    public function Cost(){
        return $this->_beverage->Cost() + 0.2;
    }
}
// Test Case
//1.拿杯咖啡
$coffee = new Coffee();
//2.加点牛奶
$coffee = new Milk($coffee);
//3.加点糖
$coffee = new Sugar($coffee);
printf("Coffee Total:%0.2f元\n",$coffee->Cost());

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