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 stub
double 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 {
@Override
public double acceptCash(double money) {
return money;
}
}
class CashRebate extends CashSuper {
private double moneyRebate = 1d;
public CashRebate(String moneyRebate) {
this.moneyRebate = Double.parseDouble(moneyRebate);
}
@Override
public 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);
}
@Override
public 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 {
@Override
public double acceptCash(double money) {
return money;
}
}
class CashRebate extends CashSuper {
private double moneyRebate = 1d;
public CashRebate(String moneyRebate) {
this.moneyRebate = Double.parseDouble(moneyRebate);
}
@Override
public 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);
}
@Override
public 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 stub
CashContext 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 {
@Override
public double acceptCash(double money) {
return money;
}
}
class CashRebate extends CashSuper {
private double moneyRebate = 1d;
public CashRebate(String moneyRebate) {
this.moneyRebate = Double.parseDouble(moneyRebate);
}
@Override
public 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);
}
@Override
public 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 stub
CashContext 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);
}
}