• 《图解设计模式》读书笔记4-2 STRATEGY模式



    Strategy模式即策略模式,在编程中,策略指的就是算法。利用此模式可以整体替换算法,即使用不同方式解决同一个问题。比如设计一个围棋程序,通过切换算法可以方便地切换AI的难度。

    示例程序

    要实现:模拟两个人用不同的策略玩猜拳游戏。

    UML

    Hand类(手势类)

    public class Hand {
        public static final int HANDVALUE_ST = 0;  // 表示石头的值
        public static final int HANDVALUE_JD = 1;  // 表示剪刀的值
        public static final int HANDVALUE_BU = 2;  // 表示布的值
        public static final Hand[] hand = {         // 表示猜拳中3种手势的实例
                new Hand(HANDVALUE_ST),
                new Hand(HANDVALUE_JD),
                new Hand(HANDVALUE_BU),
        };
        private static final String[] name = {      // 表示猜拳中手势所对应的字符串
                "石头", "剪刀", "布",
        };
        private int handvalue;                      // 表示猜拳中出的手势的值
    
        private Hand(int handvalue) {
            this.handvalue = handvalue;
        }
    
        public static Hand getHand(int handvalue) { // 根据手势的值获取其对应的实例
            return hand[handvalue];
        }
    
        public boolean isStrongerThan(Hand h) {     // 如果this胜了h则返回true
            return fight(h) == 1;
        }
    
        public boolean isWeakerThan(Hand h) {       // 如果this输给了h则返回true
            return fight(h) == -1;
        }
    
        private int fight(Hand h) {                 // 计分:平0, 胜1, 负-1
            if (this == h) {
                return 0;
            } else if ((this.handvalue + 1) % 3 == h.handvalue) {
                return 1;
            } else {
                return -1;
            }
        }
    
        public String toString() {                  // 转换为手势值所对应的字符串
            return name[handvalue];
        }
    }
    

    Strategy接口

    public interface Strategy {
        //获取下一局要出的手势
        public abstract Hand nextHand();
        //如果win为true,表示上一局赢了,否则表示上一局输了
        public abstract void study(boolean win);
    }
    

    WinningStrategy类

    如果赢了就继续出同样的手势,否则换一个手势

    public class WinningStrategy implements Strategy {
        private Random random;
        private boolean won = false;
        private Hand prevHand;
    
        public WinningStrategy(int seed) {
            random = new Random(seed);
        }
    
        public Hand nextHand() {
            if (!won) {
                prevHand = Hand.getHand(random.nextInt(3));
            }
            return prevHand;
        }
    
        public void study(boolean win) {
            won = win;
        }
    }
    
    

    ProbStrategy类

    根据以前的结果计算概率,确定这一次要出什么手势。

    算法的具体内容不是关键,我们只需要知道这是一种算法就行了。

    public class ProbStrategy implements Strategy {
        private Random random;
        private int prevHandValue = 0;
        private int currentHandValue = 0;
        private int[][] history = {
                {1, 1, 1,},
                {1, 1, 1,},
                {1, 1, 1,},
        };
        public ProbStrategy(int seed) {
            random = new Random(seed);
        }
        public Hand nextHand() {
            int bet = random.nextInt(getSum(currentHandValue));
            int handvalue = 0;
            if (bet < history[currentHandValue][0]) {
                handvalue = 0;
            } else if (bet < history[currentHandValue][0] + history[currentHandValue][1]) {
                handvalue = 1;
            } else {
                handvalue = 2;
            }
            prevHandValue = currentHandValue;
            currentHandValue = handvalue;
            return Hand.getHand(handvalue);
        }
        private int getSum(int hv) {
            int sum = 0;
            for (int i = 0; i < 3; i++) {
                sum += history[hv][i];
            }
            return sum;
        }
        public void study(boolean win) {
            if (win) {
                history[prevHandValue][currentHandValue]++;
            } else {
                history[prevHandValue][(currentHandValue + 1) % 3]++;
                history[prevHandValue][(currentHandValue + 2) % 3]++;
            }
        }
    }
    

    Player类(玩家类)

    public class Player {
        private String name;
        private Strategy strategy;
        private int wincount;
        private int losecount;
        private int gamecount;
        public Player(String name, Strategy strategy) {         // 赋予姓名和策略
            this.name = name;
            this.strategy = strategy;
        }
        public Hand nextHand() {                                // 策略决定下一局要出的手势
            return strategy.nextHand();
        }
        public void win() {                 // 胜
            strategy.study(true);
            wincount++;
            gamecount++;
        }
        public void lose() {                // 负
            strategy.study(false);
            losecount++;
            gamecount++;
        }
        public void even() {                // 平
            gamecount++;
        }
        public String toString() {
            return "[" + name + ":" + gamecount + " games, " +
                wincount + " win, " + losecount + " lose" + "]";
        }
    }
    

    测试类

    public class Main {
        public static void main(String[] args) {
            int seed1 = Integer.parseInt("888");
            int seed2 = Integer.parseInt("999");
            Player player1 = new Player("小明", new WinningStrategy(seed1));
            Player player2 = new Player("小紅", new ProbStrategy(seed2));
            for (int i = 0; i < 10000; i++) {
                Hand nextHand1 = player1.nextHand();
                Hand nextHand2 = player2.nextHand();
                if (nextHand1.isStrongerThan(nextHand2)) {
                    System.out.println("胜利:" + player1);
                    player1.win();
                    player2.lose();
                } else if (nextHand2.isStrongerThan(nextHand1)) {
                    System.out.println("失败:" + player2);
                    player1.lose();
                    player2.win();
                } else {
                    System.out.println("平局...");
                    player1.even();
                    player2.even();
                }
            }
            System.out.println("结果:");
            System.out.println(player1.toString());
            System.out.println(player2.toString());
        }
    }
    

    角色

    Strategy(策略):抽象类或接口,负责定义策略用到的方法。

    ConcreteStrategy(具体的策略):具体的策略类,继承Strategy接口,实现其中的方法。

    Context(上下文):使用策略类的角色。注意:Context类和Strategy类是聚合关系,或者说是委托关系。

    模式的类图:

    想法

    这个模式的实现非常简单:Context使用委托这种弱关联关系,方便地实现算法的整体替换。

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  • 原文地址:https://www.cnblogs.com/qianbixin/p/10992927.html
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