策略模式+工厂模式优化if...else if...else if结构

首先，按照if...else if语句来实现打折商品的例子，代码如下：

public class Example {
 
   
    public Double calRecharge(Double charge ,RechargeTypeEnum type ){
      
       if(type.equals(RechargeTypeEnum.E_BANK)){
           return charge*0.85;
       }else if(type.equals(RechargeTypeEnum.BUSI_ACCOUNTS)){
           return charge*0.90;
       }else if(type.equals(RechargeTypeEnum.MOBILE)){
           return charge;
       }else if(type.equals(RechargeTypeEnum.CARD_RECHARGE)){
           return charge+charge*0.01;
       }else{
           return null;
       }
 
    }
   
}

用策略+工厂模式优化：

枚举类：

package strategy;
 
public enum RechargeTypeEnum {
 
    E_BANK(1, "网银"),
   
    BUSI_ACCOUNTS(2, "商户账号"),
   
    MOBILE(3,"手机卡充值"),
   
    CARD_RECHARGE(4,"充值卡");
   
    private int value;
   
    private String description;
   
    private RechargeTypeEnum(int value, String description) {
       this.value = value;
       this.description = description;
    }
      
    public int value() {
       return value;
    }
    public String description() {
       return description;
    }
   
    public static RechargeTypeEnum valueOf(int value) {
        for(RechargeTypeEnum type : RechargeTypeEnum.values()) {
            if(type.value() == value) {
                return type;
            }
        }
        return null;
    }
}

策略接口：

package strategy.strategy;
 
import strategy.RechargeTypeEnum;
 
 
public interface Strategy {
 
   
    public Double calRecharge(Double charge ,RechargeTypeEnum type );
}

策略具体实现类：

package strategy.strategy;
 
import strategy.RechargeTypeEnum;
 
public class EBankStrategy implements Strategy{
 
    @Override
    public Double calRecharge(Double charge, RechargeTypeEnum type) {
       return charge*0.85;
    }
 
}

package strategy.strategy;
 
import strategy.RechargeTypeEnum;
 
public class BusiAcctStrategy implements Strategy{
 
    @Override
    public Double calRecharge(Double charge, RechargeTypeEnum type) {
       // TODO Auto-generated method stub
       return charge*0.90;
    }
 
}

package strategy.strategy;
 
import strategy.RechargeTypeEnum;
 
public class MobileStrategy implements Strategy {
 
    @Override
    public Double calRecharge(Double charge, RechargeTypeEnum type) {
       // TODO Auto-generated method stub
       return charge;
    }
 
}

package strategy.strategy;
 
import strategy.RechargeTypeEnum;
 
public class CardStrategy implements Strategy{
 
    @Override
    public Double calRecharge(Double charge, RechargeTypeEnum type) {
       return charge+charge*0.01;
    }
 
}

策略上下文：

package strategy.strategy;
 
import strategy.RechargeTypeEnum;
 
 
public class Context {
 
    private Strategy strategy;
   
    public Double calRecharge(Double charge, Integer type) {
       strategy = StrategyFactory.getInstance().creator(type);
       return strategy.calRecharge(charge, RechargeTypeEnum.valueOf(type));
    }
 
    public Strategy getStrategy() {
       return strategy;
    }
 
    public void setStrategy(Strategy strategy) {
       this.strategy = strategy;
    }
   
}

工厂类：

package strategy.strategy;
 
import java.util.HashMap;
import java.util.Map;
 
import strategy.RechargeTypeEnum;
 
public class StrategyFactory {
 
    private static StrategyFactory factory = new StrategyFactory();
    private StrategyFactory(){
    }
    private static Map strategyMap = new HashMap<>();
    static{
       strategyMap.put(RechargeTypeEnum.E_BANK.value(), new EBankStrategy());
       strategyMap.put(RechargeTypeEnum.BUSI_ACCOUNTS.value(), new BusiAcctStrategy());
       strategyMap.put(RechargeTypeEnum.MOBILE.value(), new MobileStrategy());
       strategyMap.put(RechargeTypeEnum.CARD_RECHARGE.value(), new CardStrategy());
    }
    public Strategy creator(Integer type){
       return strategyMap.get(type);
    }
    public static StrategyFactory getInstance(){
       return factory;
    }
}

客户端类：

package strategy.strategy;
 
import strategy.RechargeTypeEnum;
 
public class Client {
 
   
    public static void main(String[] args) {
 
       Context context = new Context();
       // 网银充值100 需要付多少
       Double money = context.calRecharge(100D,
              RechargeTypeEnum.E_BANK.value());
       System.out.println(money);
 
       // 商户账户充值100 需要付多少
       Double money2 = context.calRecharge(100D,
              RechargeTypeEnum.BUSI_ACCOUNTS.value());
       System.out.println(money2);
 
       // 手机充值100 需要付多少
       Double money3 = context.calRecharge(100D,
              RechargeTypeEnum.MOBILE.value());
       System.out.println(money3);
 
       // 充值卡充值100 需要付多少
       Double money4 = context.calRecharge(100D,
              RechargeTypeEnum.CARD_RECHARGE.value());
       System.out.println(money4);
    }
 
}

运行结果：

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85.0

90.0

100.0

101.0

从上面代码可以看出，策略模式把具体的算法封装到了具体策略角色内部，增强了可扩展性，隐蔽了实现细节；它替代继承来实现，避免了 if- else 这种不易维护的条件语句。当然我们也可以看到，策略模式由于独立策略实现，使得系统内增加了很多策略类；对客户端来说必须知道兜友哪些具体策略，而且需要知道选择具体策略的条件。

策略模式+工厂模式优化if...else if...else if结构

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