Enums ()方法实现

Question

我有一个例子，我对输出感到困惑。

 enum Seasons {
    WINTER,
    SUMMER,
    SPRING,
    AUTUMN;
}
public class SeasonTest{
    public static void main(String[] args) {
    Seasons season1 = Seasons.WINTER;
    Seasons season2 = Seasons.SUMMER;
    Seasons season3 = Seasons.SPRING;
    Seasons season4 = Seasons.AUTUMN;
    System.out.println(season1.compareTo(season2));
    System.out.println(season3.compareTo(season4));
    System.out.println(season4.compareTo(season3));
    System.out.println(season2.compareTo(season1));
    System.out.println(season3.compareTo(season3));
    System.out.println(season1.compareTo(season4));
}
}

最后一行返回-3。为什么会这样呢？它应该返回-1，因为season1小于season4。为什么它会回来-3？

谢谢。

Answer 1

允许compareTo()返回任何正数、负数或零。

它不需要具体返回+/- 1。

Answer 2

Enum compareTo()是减除序数值，所以在您的示例中它是WINTER.ordinal() - AUTUMN.ordinal() = 0 - 3 = -3

Answer 3

假设元素是整数排序的，

 enum Seasons {
    WINTER,   // 0  \
    SUMMER,   // 1   \
    SPRING,   // 2    \
    AUTUMN;   // 3   --- difference is 3 (subtraction gives -3)
}