策略模式中体现了两个非常基本的面向对象设计的原则:
1.封装变化的概念2.编程中使用接口,而不是对接口的实现
策略模式的组成
1.抽象策略角色:策略类,接口或这抽象类
2.具体策略角色:实现或继承了接口或抽象类的实现类,包装了相关的算法和行为
3.环境角色:持有一个策略类的引用,最终给客户端调用
4.客户端
策略模式的实现:
环境类负责维持和查询具体策略类,由于算法和环境独立开来,算法的修改都不会影响环境和客户端。
策略模式的编写步骤:
1.对策略对象定义一个公共接口
2.编写策略类,实现接口
3.编写环境类:在使用策略对象的类中保存一个对策略对象的引用
4.在环境类中实现对策略对象的set和get方法,或者使用构造方法完成赋值
5.最后编写客户端访问环境类和策略类
//策略模式的接口
public interface Strategy
{
public int calculate(int a, int b);
}
//加减乘除四个具体策略类
public class AddStrategy implements Strategy
{
public int calculate(int a, int b)
{
return a + b;
}
}
public class SubtractStrategy implements Strategy
{
public int calculate(int a, int b)
{
return a - b;
}
}
public class MultiplyStrategy implements Strategy
{
public int calculate(int a, int b)
{
return a * b;
}
}
public class DivideStrategy implements Strategy
{
public int calculate(int a, int b)
{
return a / b;
}
}
//环境类
public class Environment
{
private Strategy strategy;
public Environment(Strategy strategy)
{
this.strategy = strategy;
}
public Strategy getStrategy()
{
return strategy;
}
public void setStrategy(Strategy strategy)
{
this.strategy = strategy;
}
public int calculate(int a ,int b)
{
return strategy.calculate(a , b);
}
}
//客户端
public class Client
{
public static void main(String[] args)
{
AddStrategy addStrategy = new AddStrategy();
Environment environment = new Environment(addStrategy);
System.out.println(environment.calculate(3, 4));
SubtractStrategy subtractStrategy = new SubtractStrategy();
environment.setStrategy(subtractStrategy);
System.out.println(environment.calculate(3, 4));
MultiplyStrategy multiplyStrategy = new MultiplyStrategy();
environment.setStrategy(multiplyStrategy);
System.out.println(environment.calculate(3, 4));
DivideStrategy divideStrategy = new DivideStrategy();
environment.setStrategy(divideStrategy);
System.out.println(environment.calculate(3, 4));
}
}