查看“策略模式”的源代码

IStrategy.java<syntaxhighlight lang="java">
public interface IStrategy {

	public void operate();
	
}
</syntaxhighlight>BackDoor.java<syntaxhighlight lang="java">
/**
 * 乔国老开后门
 */
public class BackDoor implements IStrategy {

	@Override
	public void operate() {
		System.out.println("找乔国老帮忙，让吴国太给孙权施加压力");
	}

}
</syntaxhighlight>GivenGreenLight.java<syntaxhighlight lang="java">
/**
 * 吴国太开绿灯
 */
public class GivenGreenLight implements IStrategy {

	@Override
	public void operate() {
		System.out.println("求吴国太开绿灯，放行！");
	}

}
</syntaxhighlight>BlockEnemy.java<syntaxhighlight lang="java">
/**
 * 孙夫人断后
 */
public class BlockEnemy implements IStrategy {

	@Override
	public void operate() {
		System.out.println("孙夫人断后，挡住追兵");
	}

}
</syntaxhighlight>Context.java<syntaxhighlight lang="java">
/**
 * 锦囊
 */
public class Context {

	
	private IStrategy strategy;
	
	public Context(IStrategy strategy) {
		this.strategy = strategy;
	}
	
	public void operate() {
		this.strategy.operate();
	}
	
}
</syntaxhighlight>ZhaoYun.java<syntaxhighlight lang="java">
public class ZhaoYun {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		Context context;
		//刚刚到吴国的时候拆一个
		System.out.println("---刚刚到吴国的时候拆第一个---");
		context = new Context(new BackDoor()); //拿到妙计
		context.operate(); //拆开执行
		System.out.println("\n\n\n\n\n\n");
		
		System.out.println("---刘备乐不思蜀了，拆第二个了---");
		context = new Context(new GivenGreenLight()); //拿到妙计
		context.operate(); //执行了第二个锦囊
		System.out.println("\n\n\n\n\n\n");
		
		System.out.println("---孙权的小兵追来了，咋办？拆第三个---");
		context = new Context(new BlockEnemy());
		context.operate();
		System.out.println("\n\n\n\n\n");
		
	}

}
</syntaxhighlight>

==== 策略模式的定义 ====
Define a family of algorithms, encapsulate each one, and make them interchangeable.

定义一组算法，将每个算法都封装起来，并且使它们之间可以互换。


策略模式使用的就是面向对象的继承和多态机制，策略模式主要有三个角色：

* Context 封装角色，也叫作上下文角色，起承上启下封装作用，屏蔽高层模块对策略、算法的直接访问，封装可能存在的变化。
* Strategy 抽象策略角色，策略、算法家族的抽象，通常为接口，定义每个策略或算法必须具有的方法和属性。
* ConcreteStrategy 具体策略角色，实现抽象策略中的操作，该类还有具体的算法。

=== 策略模式的通用源码 ===
Strategy.java<syntaxhighlight lang="java">
public interface Strategy {

	//策略模式的运算法则
	public void doSomething();
	
}
</syntaxhighlight>ConcreteStrategy1.java<syntaxhighlight lang="java">
public class ConcreteStrategy1 implements Strategy {

	@Override
	public void doSomething() {
		System.out.println("具体策略1的运算法则");
	}

}
</syntaxhighlight>ConcreteStrategy2.java<syntaxhighlight lang="java">
public class ConcreteStrategy2 implements Strategy {

	@Override
	public void doSomething() {
		System.out.println("具体策略2的运算法则");
	}

}
</syntaxhighlight>Context.java<syntaxhighlight lang="java">
/**
 * 封装角色
 */
public class Context {

	//抽象策略
	private Strategy strategy = null;

	//构造函数设置具体策略
	public Context(Strategy _strategy) {
		this.strategy = _strategy;
	}
	
	//封装后的策略方法
	public void doAnything() {
		this.strategy.doSomething();
	}
	
}

</syntaxhighlight>Client.java<syntaxhighlight lang="java">
public class Client {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		//声明一个具体策略
		Strategy strategy = new ConcreteStrategy1();
		//声明上下文对象
		Context context = new Context(strategy);
		//执行封装后的方法
		context.doAnything();
	}

}
</syntaxhighlight>