为什么“最终静态int”可以用作开关的常数，而不是“最终静态”，你的枚举“ [英] Why "final static int" can be used as a switch's case constant but not "final static <your enum>"

问题描述

为什么这个int开关有效：

Why is this int switch valid:

public class Foo {
    private final static int ONE = 1;
    private final static int TWO = 2;

    public static void main(String[] args) {
        int value = 1;
        switch (value) {
            case ONE: break;
            case TWO: break;
        }
    }

}

枚举开关不是：

import java.lang.annotation.RetentionPolicy;

public class Foo {
    private final static RetentionPolicy RT = RetentionPolicy.RUNTIME;
    private final static RetentionPolicy SRC = RetentionPolicy.SOURCE;

    public static void main(String[] args) {
        RetentionPolicy value = RetentionPolicy.RUNTIME;
        switch (value) {
            case RT: break;
            case SRC: break;
        }
    }

}

我知道在这种情况下，必须是一个常量，所以为什么我可以使用一个final static int作为常量，而不是final static<你的枚举>？

I know that what goes in the case must be a constant, so why can I use a "final static int" as constant but not a "final static <your enum>"?

推荐答案

因为case语句标签必须有编译时常数或EnumConstantName。 JLS 14.11

Because a case statement label must have either a compile time constant or an EnumConstantName. JLS 14.11

编译时间常数只能是字符串和原始类型，如 JLS 15.28 。因此，您不能使用静态的最终<您的枚举>，因为它既不是编译时常数也不是枚举的名称。

Compile time constants can only be strings and primitive types, as described by JLS 15.28. Thus you can not use a static final <your enum>, as it is neither a compile time constant, nor the name of an enum.

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