它也属于行为型模式的一种，在这种模式下，一个类的行为或其算法可以在运行时更改。简单实现

环境类（对外提供统一接口）

public class Context {
    private Strategy strategy;

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

    public int request(int req) {
        return state.doAction(req);
    }
}

策略接口

interface Strategy {
    int doAction(int req);
}

具体策略

public class AddStrategy implements Strategy{

    @Override
    public int doAction(int req) {
        return req + req;
    }
}

public class MultiStrategy implements Strategy{
    @Override
    public int doAction(int req) {
        return req * req;
    }
}

测试类

    public static void main(String[] args) {
        Strategy strategy= new Strategy();
        strategy.setStrategy(new AddStrategy ());
        System.out.println(context.request(10));
        strategy.setStrategy(new MultiStrategy ());
        System.out.println(context.request(10));
    }