Question

我试图手动测试我的枚举旋转方法next（）但它没有返回任何东西，很可能是null。当我分配一些变量tester = Rotation.CW0然后调用方法next（）时，该方法应返回CW90，但它不返回任何内容。 COul请smb看看我在代码中做错了什么？

public class Tester {

    public static void main(String[] args)
    {
        Rotation tester = Rotation.CW0;
        tester.next();
    }
}
public enum Rotation {

    CW0, CW90, CW180, CW270;

    // Calling rot.next() will return the next enumeration element
    // representing the next 90 degree clock-wise rotation after rot.
    public Rotation next()
    {
        if(this == CW0)
            return CW90;
        else if(this == CW90)
            return CW180;
        else if(this == CW180)
            return CW270;
        else if(this == CW270)
            return CW0;

        return null;
    }

Answer 1

public class Tester {

    public static void main(String[] args) {
        Rotation tester = Rotation.CW0;
        System.out.println(tester.next());
    }
}

public enum Rotation {

    CW0, CW90, CW180, CW270;

    public Rotation next() {
        switch (this) {
        case CW0:
           return CW90;
        case CW90:
           return CW180;
        case CW180:
           return CW270;
        case CW270:
           return CW0;
        }
        return null;
    }
}

Answer 2

怎么样：

enum Rotation {

    CW0, CW90, CW180, CW270;

    //here we know that that all enum variables are already created
    //so we can now set them up
    static{
        CW0.next = CW90;
        CW90.next = CW180;
        CW180.next = CW270;
        CW270.next = CW0;
    }

    private Rotation next;

    public Rotation next() {
        return this.next;
    }
}

或者更加神秘

enum Rotation {

    CW0, CW90, CW180, CW270;

    //to prevent recreating array of values in each `next()` call
    private static final Rotation[] values = values();
    private static final int LENGTH = values.length;

    public Rotation next() {
        return values[(this.ordinal() + 1) % LENGTH];
    }
}

但它没有给我任何回报，

好tester.next();代码会返回一些内容，但您不会在任何地方存储和使用它，因此可能会将代码更改为

Rotation tester = Rotation.CW0;
System.out.println(tester.next());

Answer 3

将next（）的结果分配给测试人员：

public static void main(String[] args) throws Exception {
    Rotation tester = Rotation.CW0;
    tester = tester.next();
    System.out.println(tester);
}

public enum Rotation {

    CW0, CW90, CW180, CW270;

    // Calling rot.next() will return the next enumeration element
    // representing the next 90 degree clock-wise rotation after rot.
    public Rotation next() {
        if (this == CW0) {
            return CW90;
        } else if (this == CW90) {
            return CW180;
        } else if (this == CW180) {
            return CW270;
        } else if (this == CW270) {
            return CW0;
        }

        return null;
    }
}

试图测试Enum的方法

3 个答案: