设计模式之策略模式
jopen 9年前
设计模式之策略模式
什么是策略模式?
策略模式定义了算法家族,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,不会影响到使用算法的客户。
UML
下面用具体代码来解释该模式
首先定义所有支持的算法的公共接口,Strategy接口
package strategy; public interface Strategy { void algorithmInterface(); }
其次定义封装了具体算法或行为接口实现类ABC
package strategy; public class ConcreteStrategyA implements Strategy { @Override public void algorithmInterface() { // TODO Auto-generated method stub System.out.println("A"); } }
package strategy; public class ConcreteStrategyB implements Strategy { @Override public void algorithmInterface() { // TODO Auto-generated method stub System.out.println("B"); } }
package strategy; public class ConcreteStrategyC implements Strategy { @Override public void algorithmInterface() { // TODO Auto-generated method stub System.out.println("C"); } }
接着定义一个Context上下文,用一个具体的ConcreteStrategy来配置,维护一个对Strategy对象的引用
package strategy; public class Context { Strategy strategy; public Context(Strategy strategy) { // TODO Auto-generated constructor stub this.strategy=strategy; } public void contextInterface() { strategy.algorithmInterface(); } }
最后就是定义Test测试类了
package strategy; public class Test { public static void main(String[] args) { Context contextA=new Context(new ConcreteStrategyA()); contextA.contextInterface(); Context contextB=new Context(new ConcreteStrategyB()); contextB.contextInterface(); Context contextC=new Context(new ConcreteStrategyC()); contextC.contextInterface(); } }
大功告成了么?
是不是觉得怪怪的?
此时程序又变成了很早之前的套路,也就是在客户端去判断用什么算法。那么有什么方法将判断转移出去呢?
下面将其与简单工厂模式进行结合
改造Context类
package strategy; public class ContextUpdate { Strategy strategy; public ContextUpdate(String type) { // TODO Auto-generated constructor stub switch (type) { case "A": strategy =new ConcreteStrategyA(); break; case "B": strategy =new ConcreteStrategyB(); break; default: strategy =new ConcreteStrategyC(); break; } } public void concreteStrategy() { strategy.algorithmInterface(); } }
此时判断便从客户端转移出去了
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