一、枚举类型——使用 EnumMap 分发

news2024/11/16 13:26:43

使用 EnumMap 可以实现“真正的”双路分发，它是专门为 enum 设计的高效 Map。我们的目标是在两个未知类型中切换，因此由 EnumMap 组成的 EnumMap （嵌套 EnumMap ）可以实现双路分发。

RoShamBo5.java

import java.util.EnumMap;

import static enums.TEST0006.Outcome.*;

enum RoShamBo5 implements Competitor<RoShamBo5> {
    PAPER, SCISSORS, ROCK;
    static EnumMap<RoShamBo5, EnumMap<RoShamBo5, Outcome>> table = new EnumMap<>(RoShamBo5.class);

    static {
        for (RoShamBo5 it : RoShamBo5.values()) {
            table.put(it, new EnumMap<>(RoShamBo5.class));
        }
        initRow(PAPER, DRAW, LOSE, WIN);
        initRow(SCISSORS, WIN, DRAW, LOSE);
        initRow(ROCK, LOSE, WIN, DRAW);
    }

    static void initRow(RoShamBo5 it,Outcome vPAPER, Outcome vSCISSORS, Outcome vROCK) {
        EnumMap<RoShamBo5, Outcome> row =RoShamBo5.table.get(it);
        row.put(RoShamBo5.PAPER, vPAPER);
        row.put(RoShamBo5.SCISSORS, vSCISSORS);
        row.put(RoShamBo5.ROCK, vROCK);
    }

    @Override
    public Outcome compete(RoShamBo5 it) {
        return table.get(this).get(it);
    }

    public static void main(String[] args) {
        RoShamBo.play(RoShamBo5.class, 20);
    }
}

Competitor.java

public interface Competitor<T extends Competitor<T>> {
    Outcome compete(T competitor);
}

Outcome.java

public enum Outcome {WIN, LOSE, DRAW}

Enums.java

import java.util.Random;

public class Enums {
    private static Random rand = new Random(47);

    public static <T extends Enum<T>> T random(Class<T> ec) {
        return random(ec.getEnumConstants());
    }

    public static <T> T random(T[] values) {
        return values[rand.nextInt(values.length)];
    }
}

RoShamBo.java

public class RoShamBo {
    public static <T extends Competitor<T>>
    void match(T a, T b) {
        System.out.println(a + " vs. " + b + ": " + a.compete(b));
    }

    public static <T extends Enum<T> & Competitor<T>>
    void play(Class<T> rsbClass, int size) {
        for (int i = 0; i < size; i++) {
            match(Enums.random(rsbClass), Enums.random(rsbClass));
        }
    }
}