大话设计模式之策略模式

应用案例：商场促销的多样性（折扣，满减）

package Strategy;//简单工厂模式实现public class CashFactory {public static CashSuper createCashAccept(String type) {CashSuper cs = null;switch(type) {case "正常收费":cs = new CashNormal();break;case "满300返100":cs = new CashReturn("300","100");break;case "打8折":cs = new CashRebate("0.8");break;}return cs;}/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubdouble total = 0.0d,totalprice = 1000d;CashSuper csuper = CashFactory.createCashAccept("正常收费");total = csuper.acceptCash(totalprice);System.out.println(total);total = 0.0d;totalprice = 1000d;csuper = CashFactory.createCashAccept("满300返100");total = csuper.acceptCash(totalprice);System.out.println(total);total = 0.0d;totalprice = 1000d;csuper = CashFactory.createCashAccept("打8折");total = csuper.acceptCash(totalprice);System.out.println(total);}}abstract class CashSuper {public abstract double acceptCash(double money);}class CashNormal extends CashSuper {@Overridepublic double acceptCash(double money) {return money;}}class CashRebate extends CashSuper {private double moneyRebate = 1d;public CashRebate(String moneyRebate) {this.moneyRebate = Double.parseDouble(moneyRebate);}@Overridepublic double acceptCash(double money) {return money * moneyRebate;}}class CashReturn extends CashSuper {private double moneyCondition = 0.0d;private double moneyReturn = 0.0d;public CashReturn(String moneyCondition, String moneyReturn) {this.moneyCondition = Double.parseDouble(moneyCondition);this.moneyReturn = Double.parseDouble(moneyReturn);}@Overridepublic double acceptCash(double money) {double result = money;if (money >= moneyCondition) {result = money - Math.floor(money/this.moneyCondition) * this.moneyReturn; }return result;}}

采用简单工厂模式的缺陷：促销方式的修改经常需要修改工厂，代码需要经常重新编译部署代码

策略模式：它定义了算法家族，分别封装起来，让它们之间可以相互替换，此模式让算法的变化，不会影响到使用的算法客户。

Context是一个配置管理类，持有一个Strategy抽象类对象，构造函数用于初始化该对象，Context封装了Strategy的抽象方法调用。

简言之，以算法类为参数配置管理类，配置管理类对算法调用进行了封装

package Strategy;abstract class CashSuper {public abstract double acceptCash(double money);}class CashNormal extends CashSuper {@Overridepublic double acceptCash(double money) {return money;}}class CashRebate extends CashSuper {private double moneyRebate = 1d;public CashRebate(String moneyRebate) {this.moneyRebate = Double.parseDouble(moneyRebate);}@Overridepublic double acceptCash(double money) {return money * moneyRebate;}}class CashReturn extends CashSuper {private double moneyCondition = 0.0d;private double moneyReturn = 0.0d;public CashReturn(String moneyCondition, String moneyReturn) {this.moneyCondition = Double.parseDouble(moneyCondition);this.moneyReturn = Double.parseDouble(moneyReturn);}@Overridepublic double acceptCash(double money) {double result = money;if (money >= moneyCondition) {result = money - Math.floor(money / this.moneyCondition)* this.moneyReturn;}return result;}}public class CashContext {private CashSuper cs;public CashContext(CashSuper csuper) {this.cs = csuper;}public double GetResult(double money) {return cs.acceptCash(money);}public static void main(String[] args) {// TODO Auto-generated method stubCashContext cc = null;String type = "正常收费";switch(type) {case "正常收费":cc = new CashContext(new CashNormal());break;case "满300返100":cc = new CashContext(new CashReturn("300","100"));break;case "打8折":cc = new CashContext(new CashRebate("0.8"));break;}double total = 0.0d,totalprice = 1000d;total = cc.GetResult(totalprice);System.out.println(total);total = 0.0d;totalprice = 1000d;cc = new CashContext(new CashReturn("300","100"));total = cc.GetResult(totalprice);System.out.println(total);total = 0.0d;totalprice = 1000d;cc = new CashContext(new CashRebate("0.8"));total = cc.GetResult(totalprice);System.out.println(total);}}

策略与简单工厂的结合：

还是通过配置类，配置算法类，只是在内部用工厂方法产生

package Strategy;abstract class CashSuper {public abstract double acceptCash(double money);}class CashNormal extends CashSuper {@Overridepublic double acceptCash(double money) {return money;}}class CashRebate extends CashSuper {private double moneyRebate = 1d;public CashRebate(String moneyRebate) {this.moneyRebate = Double.parseDouble(moneyRebate);}@Overridepublic double acceptCash(double money) {return money * moneyRebate;}}class CashReturn extends CashSuper {private double moneyCondition = 0.0d;private double moneyReturn = 0.0d;public CashReturn(String moneyCondition, String moneyReturn) {this.moneyCondition = Double.parseDouble(moneyCondition);this.moneyReturn = Double.parseDouble(moneyReturn);}@Overridepublic double acceptCash(double money) {double result = money;if (money >= moneyCondition) {result = money - Math.floor(money / this.moneyCondition)* this.moneyReturn;}return result;}}public class CashContext {private CashSuper cs;public CashContext(String type) {switch(type) {case "正常收费":cs = new CashNormal();break;case "满300返100":cs = new CashReturn("300","100");break;case "打8折":cs =new CashRebate("0.8");break;}}public double GetResult(double money) {return cs.acceptCash(money);}public static void main(String[] args) {// TODO Auto-generated method stubCashContext cc = null;double total = 0.0d,totalprice = 1000d;cc = new CashContext("正常收费");total = cc.GetResult(totalprice);System.out.println(total);total = 0.0d;totalprice = 1000d;cc = new CashContext("满300返100");total = cc.GetResult(totalprice);System.out.println(total);total = 0.0d;totalprice = 1000d;cc = new CashContext("打8折");total = cc.GetResult(totalprice);System.out.println(total);}}