设计模式 - 策略模式(Strategy Pattern) 详解

策略模式(Strategy Pattern) 详解

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策略模式: 定义了算法族, 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独立于使用算法的客户.

对于父类的子类族需要经常扩展新的功能, 为了使用父类比较灵活的添加子类, 把父类的行为写成接口(interface)的形式;

使用set()方法, 重新设定接口的行为. 提供行为的调用的方法(如perform), 需要调用接口(interface)的固有方法(fly & quack)即可.

代码:

package strategy;

public abstract class Duck { //抽象类
	FlyBehavior flyBehavior;
	QuackBehavior quackBehavior;

	public Duck() { //构造函数
	}

	public abstract void display(); //抽象函数

	public void performFly() {
		flyBehavior.fly();
	}

	public void performQuack() {
		quackBehavior.quack();
	}

	public void swim() {
		System.out.println("All ducks float, even decoys! ");
	}

	public void setFlyBehavior(FlyBehavior fb) {
		flyBehavior = fb;
	}

	public void setQuackBehavior(QuackBehavior qb) {
		quackBehavior = qb;
	}
}

FlyBehavior 和 QuackBehavior是两个接口(interface), 包含方法fly()和quack();

继承接口的方法, 都必须使用fly()和quack()的方法;

代码:

/**
 * @time 2014.5.22
 */
package strategy;

/**
 * @author C.L.Wang
 *
 */
public interface FlyBehavior {
	public void fly();
}

/**
 * @time 2014.5.22
 */
package strategy;

/**
 * @author C.L.Wang
 *
 */
public interface QuackBehavior {
	public void quack();
}

接口的实现.

代码:

/**
 * @time 2014.5.22
 */
package strategy;

/**
 * @author C.L.Wang
 *
 */
public class FlyNoWay implements FlyBehavior {

	/* (non-Javadoc)
	 * @see strategy.FlyBehavior#fly()
	 */
	@Override
	public void fly() {
		// TODO Auto-generated method stub
		System.out.println("I can't fly! ");
	}

}

/**
 *
 */
package strategy;

/**
 * @author Administrator
 *
 */
public class FlyRocketPowerd implements FlyBehavior {

	/* (non-Javadoc)
	 * @see strategy.FlyBehavior#fly()
	 */
	@Override
	public void fly() {
		// TODO Auto-generated method stub
		System.out.println("I'm flying with a rocket! ");
	}

}

/**
 *
 */
package strategy;

/**
 * @author Administrator
 *
 */
public class FlyRocketPowerd implements FlyBehavior {

	/* (non-Javadoc)
	 * @see strategy.FlyBehavior#fly()
	 */
	@Override
	public void fly() {
		// TODO Auto-generated method stub
		System.out.println("I'm flying with a rocket! ");
	}

}

/**
 *
 */
package strategy;

/**
 * @author Administrator
 *
 */
public class MuteQuack implements QuackBehavior {

	/* (non-Javadoc)
	 * @see strategy.QuackBehavior#quack()
	 */
	@Override
	public void quack() {
		// TODO Auto-generated method stub
		System.out.println("<< Silence >>");
	}

}

/**
 *
 */
package strategy;

/**
 * @author Administrator
 *
 */
public class Quack implements QuackBehavior {

	/* (non-Javadoc)
	 * @see strategy.QuackBehavior#quack()
	 */
	@Override
	public void quack() {
		// TODO Auto-generated method stub
		System.out.println("Quack! ");
	}

}

/**
 *
 */
package strategy;

/**
 * @author Administrator
 *
 */
public class Squeak implements QuackBehavior {

	/* (non-Javadoc)
	 * @see strategy.QuackBehavior#quack()
	 */
	@Override
	public void quack() {
		// TODO Auto-generated method stub
		System.out.println("Squeak");
	}

}

继承父类的子类, 只需要指定所使用的行为(即 接口(interface)的实现)的类型, 并提供自己的display()函数即可;

代码:

/**
 *
 */
package strategy;

/**
 * @author Administrator
 *
 */
public class MallardDuck extends Duck {

	public MallardDuck() {
		quackBehavior = new Quack();
		flyBehavior = new FlyWithWings();
	}

	/* (non-Javadoc)
	 * @see strategy.Duck#display()
	 */
	@Override
	public void display() {
		// TODO Auto-generated method stub
		System.out.println("I'm a real Mallard duck! ");
	}

}

/**
 *
 */
package strategy;

/**
 * @author Administrator
 *
 */
public class ModelDuck extends Duck {

	public ModelDuck() {
		flyBehavior = new FlyNoWay();
		quackBehavior = new Quack();
	}

	/* (non-Javadoc)
	 * @see strategy.Duck#display()
	 */
	@Override
	public void display() {
		// TODO Auto-generated method stub
		System.out.println("I'm a model duck. ");
	}

}

执行时, 只需要执行各个子类继承父类的方法(perform), 即可, 也可以使用set()方法改变其行为;

代码:

/**
 *
 */
package strategy;

/**
 * @author Administrator
 *
 */
public class MiniDuckSimulator {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Duck mallard = new MallardDuck();
		mallard.performQuack();
		mallard.performFly();

		Duck model = new ModelDuck();
		model.performFly();
		model.performQuack();

		model.setFlyBehavior(new FlyRocketPowerd());
		model.performFly();
	}

}

面向对象的原则:

1. 封装变化的部分;

2. 多用组合, 少用继承;

3. 针对接口编程, 不针对实现编程;

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