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#设计原则

类应该对扩展开放, 对修改关闭

#装饰者模式(Decorator Pattern)

装饰者模式动态地将责任附加到对象上, 若要扩展功能, 装饰者提供了比继承更有弹性的替代方案.

  • 每个装饰者都包装一个组件(类), 装饰者有一个实例变量保存这个组件的引用(类的引用)
  • 组件: 被装饰者
  • 装饰者: 本身为对象, 以组件为参数, 返回装饰后的对象
  • 装饰器和组件有共同的超类
  • 组件可以被多个装饰者装饰
  • 具体装饰者使用继承方式
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// 被装饰的类
// 抽象类, 并包含抽象方法cost
public abstract class Beverage {
    String description = "Unknown Beverage";
    public String getDescription() {
        return description;
    }
    public abstract double cost();
    
}
// Beverage具体子类
public class Espresso extends Beverage {
    public Espresso() {
        description = "Espresso";
    }
    public double cost() {
        return 1.99;
    }
}
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//装饰者抽象类
public abstract class CondimentDecorator extends Beverage {
    //所有装饰者都必须重新实现这个方法
    public abstract String getDescription();
}
//实现具体装饰者
public class Mocha extends CondimentDecorator {
    Beverage beverage;
    public Mocha(Beverage beverage) {
        this.beverage = beverage;
    }
    public String getDescription() {
        return beverage.getDescription() + ", Mocha";
    }
    public double cost() {
        return 0.20 + beverage.cost();
    }
}
public class Soy extends CondimentDecorator {
    Beverage beverage;
    public Soy(Beverage beverage) {
        this.beverage = beverage;
    }
    public String getDescription() {
        return beverage.getDescription() + ", Soy";
    }
    public double cost() {
        return 0.15 + beverage.cost();
    }
}
public class Whip extends CondimentDecorator {
    Beverage beverage;
    public Whip(Beverage beverage) {
        this.beverage = beverage;
    }
    public String getDescription() {
        return beverage.getDescription() + ", Whip";
    }
    public double cost() {
        return 0.10 + beverage.cost();
    }
}
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//测试装饰者
public class StarbuzzCoffee {
    public static void main(String args[]) {
        Beverage beverage = new Espresso();
        System.out.println(beverage.getDescription() + " $ " + beverage.cost());
        //制造一个Espresso对象
        Beverage beverage1 = new Espresso();
        beverage1 = new Mocha(beverage1);  // Mocha装饰这个对象
        beverage1 = new Mocha(beverage1);  // 装饰这个对象
        beverage1 = new Whip(beverage1);   // 装饰这个对象
        System.out.println(beverage1.getDescription() + " $" + beverage1.cost());
    }
}

应用场景:

适合类中各种行为的大量组合.

#工厂模式(Factory Pattern)

待更新…

#参考链接

Head First Design Pattern