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Headfirst-3 装饰者模式

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1 Headfirst-3 装饰者模式

定义：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。

1.1 模式设计原则

对扩展开放，对修改关闭

1.2 例子类图

1.1      例子代码
1 Beverage.java
package beverage;

public abstract class Beverage {
    String description = "Unknown Beverage";

    public String getDescription() {
       return description;
    }

    public abstract double cost();
}

2 CondimentDecorator.java
package beverage;

public abstract class CondimentDecorator extends Beverage {
    public abstract String getDescription();
}

3 Espresso.java
package beverage;

public class Espresso extends Beverage {

    public Espresso() {
       description = "Espresso";
    }

    public double cost() {
       return 1.99;
    }
}

4 DarkRoast.java
package beverage;

public class DarkRoast extends Beverage {
    public DarkRoast() {
       description = "Dark Roast Coffee";
    }

    public double cost() {
       return .99;
    }
}
5 HouseBlend.java
package beverage;

public class HouseBlend extends Beverage {
    public HouseBlend() {
       description = "House Blend Coffee";
    }

    public double cost() {
       return .89;
    }
}

6 Mocha.java
package beverage;

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 .20 + beverage.cost();
    }
}
7 Soy.java
package beverage;

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 .15 + beverage.cost();
    }
}
8 Whip.java
package beverage;

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 .10 + beverage.cost();
    }
}

9 StarbuzzCoffee.java
package beverage;

public class StarbuzzCoffee {

    public static void main(String args[]) {
       Beverage beverage = new Espresso();
       System.out.println(beverage.getDescription()
              + " $" + beverage.cost());

       Beverage beverage2 = new DarkRoast();
       beverage2 = new Mocha(beverage2);
       beverage2 = new Mocha(beverage2);
       beverage2 = new Whip(beverage2);
       System.out.println(beverage2.getDescription()
              + " $" + beverage2.cost());

       Beverage beverage3 = new HouseBlend();
       beverage3 = new Soy(beverage3);
       beverage3 = new Mocha(beverage3);
       beverage3 = new Whip(beverage3);
       System.out.println(beverage3.getDescription()
              + " $" + beverage3.cost());
    }
}

gis软件应用教学大纲

gis软件应用教学大纲

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