java - 随机枚举返回 null

Question

您好，我正在尝试获取随机 ENUM，但它返回 null，有人可以帮助我我的代码出了什么问题吗？我试图独自修复它，但我放弃了。

public class LotteryMachine {
    protected enum Sings {
        ONE,
        TWO,
        THREE
}

    private static final List<Sings> SINGS_LIST = Collections.unmodifiableList(Arrays.asList(Sings.values()));
    private static final int SIZE = SINGS_LIST.size();
    private static final Random RANDOM = new Random();

    Sings randomSing() {
        return SINGS_LIST.get(RANDOM.nextInt(SIZE));

    }
}


public class Game {

    private LotteryMachine lotteryMachine = new LotteryMachine();

    private LotteryMachine.Sings singOne;
    private LotteryMachine.Sings singTwo;
    private LotteryMachine.Sings singThree;

    private void Lottery(){
        this.singOne = lotteryMachine.randomSing();
        this.singTwo = lotteryMachine.randomSing();
        this.singThree = lotteryMachine.randomSing();
    }

    public void viewLottery(){
        System.out.print(singOne + " " + singTwo + " " + singThree);
    }
}

Answer 1

你的问题似乎就在这里

private void Lottery(){
    this.singOne = lotteryMachine.randomSing();
    this.singTwo = lotteryMachine.randomSing();
    this.singThree = lotteryMachine.randomSing();
}

这不是一个构造函数；相反，它是一个名为 Lottery() 的私有(private)方法，并且不被 Game 类使用。由于该方法从未被调用，因此所有 singX 字段都未初始化(即 null)。将初始化逻辑从所述方法移动到如下所示的字段声明后，事情应该可以正常工作

private LotteryMachine.Sings singOne = lotteryMachine.randomSing();
private LotteryMachine.Sings singTwo = lotteryMachine.randomSing();
private LotteryMachine.Sings singThree = lotteryMachine.randomSing();

或者也可以声明 Game 类的构造函数，如下所示:

public Game() {
    this.singOne = lotteryMachine.randomSing();
    this.singTwo = lotteryMachine.randomSing();
    this.singThree = lotteryMachine.randomSing();
}