Java封装商场打折策略(Strategy模式)

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有了OO的基础后，开始认真学习设计模式。

首先学习的是Strategy，下面就封装商场打折策略来分析下策略模式是怎样一回事。

商场每逢节假日都会对不同的商品采用不同的打折策略，首先卖苹果的说我的苹果要打折，好的，我们建立Market和Apple类。

 1 /** 2  *  3  * @author LingJian 4  * 5  */ 6 public class Market { 7  8     /** 9      * 只对Apple10      * @param apple11      */12     public static void normalSell(Apple apple) {13         System.out.println("未打折价钱:" + apple.getPrice() * apple.getWeight());14     }15     /**16      * 只对Apple17      * @param apple18      */19     public static void discountSell(Apple apple) {20         double weight = apple.getWeight();21         //打折算法22         if(weight < 10) {23             normalSell(apple);24         }else if(weight >= 10 && weight < 50) {25             System.out.println("打八八折价钱:" + apple.getPrice() * apple.getWeight() * 0.88 );26         }else if(weight >= 50) {27             System.out.println("打五折价钱:" + apple.getPrice() * apple.getWeight() * 0.5 );28         }        29     }30 }

 1 /** 2  *  3  * @author LingJian 4  * 5  */ 6 public class Apple { 7     //重量 8     private double weight; 9     //单价 实际开发中 涉及金钱等精确计算都是用BigDecimal10     private double price;11         12     public double getWeight() {13         return weight;4     }15     public void setWeight(double weight) {16         this.weight = weight;17     }18     public double getPrice() {19         return price;20     }21     public void setPrice(double price) {22         this.price = price;23     }24     public Apple(double weight, double price) {25         super();26         this.weight = weight;27         this.price = price;28     }29 30 31     32 }

/** *  * @author LingJian * */public class Test {    /**     * @param args     */    public static void main(String[] args) {        //只能对苹果打折 还不能对通用的一类事物打折 而且都是要卖什么就写什么打折算法 其实每类事物打折算法又是不一致的        Apple apple = new Apple(10.35, 3.6);        Market.normalSell(apple);        Market.discountSell(apple);    }}

节假日过了两天后，卖香蕉的一看，苹果打折促销后，原先买香蕉的都跑去买苹果了，不行，香蕉也要打折，不然卖不出去就烂了，OK，这个时候，我们再往Market加一个卖香蕉的打折方法和Banana类，问题很好的解决了….后来，卖梨卖橙子卖橘子的都来了，但是由于每个商品打折的算法和策略都不一样，咱们只能先往Market不停的加方法….显然这不是很好的设计，不停的写打折方法就说明我们这个打折方法不够通用，扩展性不强，那这个时候怎么办呢？对，肯定是想办法让咱们的打折方法通用，增强扩展性，那么说到扩展我们肯定得想到OO的核心-多态。

这里，我们创建一个Discountable接口，让需要打折的商品都实现这个接口，并且在重写打折方法，这样对于Market来说，我们就把具体的打折实现方式都交给了具体的对象本身来实现，我们就不用担心算法策略不同而不停的增加方法。

/** *  * @author LingJian * */public class Market {    /**     * 对可打折的一类事物进行打折     * @param apple     */    public static void discountSell(Discountable d) {        d.discountSell();    }        }

public class Apple implements Discountable {    //重量    private double weight;    //单价 实际开发中 涉及金钱等精确计算都是用BigDecimal    private double price;            public double getWeight() {        return weight;    }    public void setWeight(double weight) {        this.weight = weight;    }    public double getPrice() {        return price;    }    public void setPrice(double price) {        this.price = price;    }    public Apple(double weight, double price) {        super();        this.weight = weight;        this.price = price;    }        @Override    public void discountSell() {        //打折算法        if(weight < 10) {            System.out.println("Apple未打折价钱:" + weight * price);        }else if(weight >= 10 && weight < 50) {            System.out.println("Apple打八八折价钱:" + weight * price * 0.88 );        }else if(weight >= 50) {            System.out.println("Apple打五折价钱:" + weight * price * 0.5 );        }    }        }

/** *  * @author LingJian * */public class Banana implements Discountable {    //重量    private double weight;    //单价 实际开发中 涉及金钱等精确计算都是用BigDecimal    private double price;        public double getWeight() {        return weight;    }    public void setWeight(double weight) {        this.weight = weight;    }    public double getPrice() {        return price;    }    public void setPrice(double price) {        this.price = price;    }    public Banana(double weight, double price) {        super();        this.weight = weight;        this.price = price;    }        @Override    public void discountSell() {        //打折算法        if(weight < 5) {            System.out.println("Banana未打折价钱:" + weight * price);        }else if(weight >= 5 && weight < 10) {            System.out.println("Banana打八八折价钱:" + weight * price * 0.88 );        }else if(weight >= 10) {            System.out.println("Banana打五折价钱:" + weight * price * 0.5 );        }            }}

/** *  * @author LingJian * */public interface Discountable {    public void discountSell();}

/** *  * @author LingJian * */public class Test {    /**     * @param args     */    public static void main(String[] args) {        //可对打折一类事物进行打折啦 先是Apple        Discountable d = new Apple(10.35, 3.6);//        Discountable d = new Banana(10.35, 1.6);        Market.discountSell(d);    }}

OK，这一次咱们采用的都是固定的按购买量打折，但是打折的策略算法是有可能变化的，不一定每次节假日都是按购买量打折，所以咱们的打折策略不能写死了，得能够灵活的变化，怎么办呢？当然，还是多态，我们再创建一个Discountor接口，而具体的打折策略都交给具体的实现类来实现，再在需要打折的商品类中，让其持有Discountor接口的实现子类，这样不管每次打折策略怎么变化，我们只需要让打折商品持有不同的实现对象即可灵活的应对变化，这就是策略(Strategy)模式。

/** *  * @author LingJian * */public class Apple implements Discountable {    //重量    private double weight;    //单价 实际开发中 涉及金钱等精确计算都是用BigDecimal    private double price;    //按购买量打折//    private Discountor d = new AppleWeightDiscountor();    //按购买总价打折    private Discountor d = new ApplePriceDiscountor();        public double getWeight() {        return weight;    }    public void setWeight(double weight) {        this.weight = weight;    }    public double getPrice() {        return price;    }    public void setPrice(double price) {        this.price = price;    }    public Apple(double weight, double price) {        super();        this.weight = weight;        this.price = price;    }        @Override    public void discountSell() {        d.discount(this);    }        }

/** *  * @author LingJian * */public interface Discountor {    public void discount(Discountable d);}

/** *  * @author LingJian * */public class AppleWeightDiscountor implements Discountor {    /**     * 按购买量打折     */    @Override    public void discount(Discountable d) {        Apple apple = (Apple)d;        if(apple.getWeight() < 10) {            System.out.println("Apple未打折价钱:" + apple.getWeight() * apple.getPrice());        }else if(apple.getWeight() >= 10 && apple.getWeight() < 50) {            System.out.println("Apple打八八折价钱:" + apple.getWeight() * apple.getPrice() * 0.88 );        }else if(apple.getWeight() >= 50) {            System.out.println("Apple打五折价钱:" + apple.getWeight() * apple.getPrice() * 0.5 );        }            }}

/** *  * @author LingJian * */public class ApplePriceDiscountor implements Discountor {    /**     * 购买满10元立减1角     * 购买满20元立减1元     * 购买满30元立减5元     */    @Override    public void discount(Discountable d) {        Apple apple = (Apple)d;        if(apple.getWeight() * apple.getPrice() < 10) {            System.out.println("Apple未打折价钱:" + apple.getWeight() * apple.getPrice());        }else if(apple.getWeight() * apple.getPrice() >= 10 && apple.getWeight() * apple.getPrice() < 20) {            System.out.println("Apple购买满10元立减1角:" + (apple.getWeight() * apple.getPrice() - 0.1) );        }else if(apple.getWeight() * apple.getPrice() >= 20 && apple.getWeight() * apple.getPrice() < 30) {            System.out.println("Apple购买满20元立减1元:" + (apple.getWeight() * apple.getPrice() - 1) );        }else if(apple.getWeight() * apple.getPrice() >= 30) {            System.out.println("Apple购买满30元立减5元:" + (apple.getWeight() * apple.getPrice() - 5) );        }            }}

Test类无需改变。

简单的描绘下封装商场打折策略的设计图。如下所示：

Market负责给Discountable的商品打折，而具体的可打折的商品的打折的算法则交给Discountor的实现子类来具体实现。