策略模式

1.定义与类型

• 定义：定义了算法家族，别离封装起来，让他们之间能够相互转换，此模式让算法的变动不会影响到应用算法的用户
• if...else
• 类型:行为型

2.实用场景

• 零碎有很多类，而他们的区别仅仅在于他们的行为不同
• 一个零碎须要动静地在几种算法中抉择一种

3.长处

• 开闭准则
• 防止应用多种条件转移语句
• 进步算法的保密性和安全性

4.毛病

• 客户端必须晓得所有的策略类，并自行决定应用哪一个策略类
• 产生很多策略类

5.相干设计模式

• 策略模式 和 工厂模式
• 策略模式 和 状态模式

6.Coding

策略模式加工厂模式

• 创立策略接口Promotion

public interface PromotionStrategy {    void doPromotion();}

• 创立一系列促销策略

public class FanXianPromotionStrategy implements PromotionStrategy{    @Override    public void doPromotion() {        System.out.println("返现促销,返回的余额寄存到用户余额中！");    }}

public class LiJianPromotionStrategy implements PromotionStrategy {    @Override    public void doPromotion() {        System.out.println("立减促销,课程的价格间接减去配置的价格");    }}

public class ManJianPromotionStrategy implements PromotionStrategy{    @Override    public void doPromotion() {        System.out.println("满减促销：满200减20");    }}

• 创立促销流动：用来执行促销策略的类

public class PromotionActivity {      private PromotionStrategy strategy;      public PromotionActivity(PromotionStrategy strategy){        this.strategy = strategy;    }    public void executeStrategy(){        strategy.doPromotion();    }}

• 创立促销策略工厂

/** * @program: design_pattern * @description: 促销策略工厂 * @create: 2021-10-13 22:23 **/public class PromotionStrategyFactory {    /** 私有化结构器  */    private PromotionStrategyFactory(){}    private static  final Map<String,PromotionStrategy>  PROMOTION_STRATEGY_MAP = new HashMap<>();    //初始化工厂    static {        PROMOTION_STRATEGY_MAP.put(PromotionType.FANXIAN,new FanXianPromotionStrategy());        PROMOTION_STRATEGY_MAP.put(PromotionType.LIJIAN,new LiJianPromotionStrategy());        PROMOTION_STRATEGY_MAP.put(PromotionType.MANJIAN,new ManJianPromotionStrategy());    }    /** 对外提供获取策略的办法 */    public  static PromotionStrategy getPromotionStrategy(String promotionKey){        PromotionStrategy promotionStrategy = PROMOTION_STRATEGY_MAP.get(promotionKey);        return promotionStrategy == null?null:promotionStrategy;    }    private interface PromotionType{         String LIJIAN = "LIJIAN";         String MANJIAN = "MANJIAN";         String FANXIAN = "FANXIAN";    }}

• 测试类

public class Test {    public static void main(String[] args) {        String promotionKey = "LIJIAN";        PromotionActivity promotionActivity =           new PromotionActivity(PromotionStrategyFactory.getPromotionStrategy(promotionKey));        promotionActivity.executeStrategy();    }}

• 控制台输入:

7.总结

• 策略模式联合工厂模式缩小了if...else代码，进步了代码的效率和可维护性
• 代码的解耦
• 策略类中都有独特的行为，不过这个行为的后果不一样