装饰者模式

装饰者模式

**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。

*设计原则：*类应该对扩展开放，对修改关闭

继承属于扩展形式之一，但不见得是达到弹性设计的最佳方式。

在我们的设计中，应该允许行为可以被扩展，而无须修改现有的代码。

组合和委托可用在运行时动态地加上新的行为。

除了继承，装饰者模式也可以让我们扩展行为。

装饰者模式意味着一群装饰者类，这些类用来包装具体组件。

装饰者类反映着出被装饰的组件类型（事实上，他们具有相同的类型，都经过接口或继承实现）。

装饰者可以在被装饰者的行为前面（与/或）后面加上自己的行为，甚至将被装饰者的行为整个取代掉，而达到特定的目的。

你可以用无数个装饰者包装一个组件。

装饰者一般对组件的客户是透明的，除非客户程序依赖于组件的具体类型。

装饰者会导致设计中出现许多小对象，如果过度使用，会让程序变得很复杂。

package HeadFirstDesignMode.decorator;

/**
 * 描述：
 * Created by zjw on 2018-11-04 19:58
 */
public class StartBuckCoffee {

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

        Beverage beverage1 = new DarkRoast();
        beverage1 = new Mocha(beverage1);
        beverage1 = new Mocha(beverage1);
        beverage1 = new Whip(beverage1);
        System.out.println(beverage1.getDescription() + " $" + beverage1.cost());

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

    // 饮料杯型、描述、成本
    static abstract class Beverage {
        // 小杯，中杯，大杯
        public static int TALL = 1, GRANDE = 2, VENTI = 3;
        public String description = "Unknown Beverage";
        public int size = 0;

        public String getDescription() {
            return description;
        }

        public int getSize() {
            return size;
        }

        //成本
        public abstract double cost();
    }

    //装饰器
    static abstract class CondimentDecorator extends Beverage {
        public abstract String getDescription();

        public abstract int getSize();
    }

    static class DarkRoast extends Beverage {

        public DarkRoast() {
            description = "Dark Roast";
        }

        @Override
        public double cost() {
            return 0.78;
        }
    }

    static class Espresso extends Beverage {

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


        @Override
        public double cost() {
            return 1.99;
        }
    }

    static class HouseBlend extends Beverage {

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

        @Override
        public double cost() {
            return 0.89;
        }
    }

    static class Mocha extends CondimentDecorator {

        Beverage beverage;

        public Mocha(Beverage beverage) {
            this.beverage = beverage;
        }

        @Override
        public String getDescription() {
            return beverage.getDescription() + ", Mocha";
        }

        @Override
        public int getSize() {
            return beverage.getSize();
        }

        @Override
        public double cost() {
            double cost = beverage.cost();
            if (getSize() == Beverage.TALL) {
                cost += 0.1;
            } else if (getSize() == Beverage.GRANDE) {
                cost += 0.15;
            } else if (getSize() == Beverage.VENTI) {
                cost += 0.20;
            }
            return cost;
        }
    }

    static class Soy extends CondimentDecorator {

        Beverage beverage;

        public Soy(Beverage beverage) {
            this.beverage = beverage;
        }

        @Override
        public String getDescription() {
            return beverage.getDescription() + ", Soy";
        }

        @Override
        public int getSize() {
            return beverage.getSize();
        }

        @Override
        public double cost() {
            return 0.55 + beverage.cost();
        }
    }

    static class Whip extends CondimentDecorator {

        Beverage beverage;

        public Whip(Beverage beverage) {
            this.beverage = beverage;
        }

        @Override
        public String getDescription() {
            return beverage.getDescription() + ",Whip";
        }

        @Override
        public int getSize() {
            return beverage.getSize();
        }

        @Override
        public double cost() {
            return 0.88 + beverage.cost();
        }
    }
}