策略模式（Strategy Pattern）

public abstract class Strategy {
    public abstract void algorithm( );  //声明抽象算法
}

public class ConcreteStrategyA extends Strategy {
    //算法的具体实现
    public void algorithm( ) {
        //算法A
    }
}

public class Context {
    private Strategy strategy; //维持一个对抽象策略类的引用
    //注入策略对象
    public void setStrategy(Strategy strategy) {
        this.strategy= strategy;
    }
    //调用策略类中的算法
    public void algorithm( ) {
        strategy.algorithm( );
    }
}

……
Context context = new Context( );
Strategy strategy;
strategy = new ConcreteStrategyA( );
             //可在运行时指定类型，通过配置文件和反射机制实现
context.setStrategy(strategy);
context.algorithm( );
……

public class Person {

    private TravelStrategy strategy;

    public void setStrategy(TravelStrategy strategy) {
        this.strategy = strategy;
    }

    public void travel(){
        strategy.travel();
    }
}

public interface TravelStrategy {

    void travel();

}

public class BicycleStrategy implements TravelStrategy{
    @Override
    public void travel() {
        System.out.println("自行车游！");
    }
}

public class WorkStrategy implements TravelStrategy{
    @Override
    public void travel() {
        System.out.println("徒步旅行！");
    }
}

public class TrainStrategy implements TravelStrategy{
    @Override
    public void travel() {
        System.out.println("乘火车旅行！");
    }
}

public class AirplaneStategy implements TravelStrategy{
    @Override
    public void travel() {
        System.out.println("飞机旅行！");
    }
}

public class Client {
    public static void main(String[] args) {

        Person person = new Person();
        TravelStrategy strategy = (TravelStrategy) XMLUtil.getBean();
        person.setStrategy(strategy);
        person.travel();
    }

}