策略模式(Strategy Pattern) 具体解释
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策略模式: 定义了算法族, 分别封装起来, 让它们之间能够相互替换, 此模式让算法的变化独立于使用算法的客户.
对于父类的子类族须要常常扩展新的功能, 为了使用父类比較灵活的加入子类, 把父类的行为写成接口(interface)的形式;
使用set()方法, 又一次设定接口的行为. 提供行为的调用的方法(如perform), 须要调用接口(interface)的固有方法(fly & quack)就可以.
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), 包括方法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, 仅仅须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()函数就可以;
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. ");
} }
运行时, 仅仅须要运行各个子类继承父类的方法(perform), 就可以, 也能够使用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;
