为什么我不能将其他 class 的常量添加到 java 的 switch 语句中？

Question

示例：我有一个 class

public class Game {


    static class GameMode {
        public static final GameMode SURVIVAL = new GameMode();
        public static final GameMode ADVENTURE = new GameMode();
        public static final GameMode GOD = new GameMode();
    }

    GameMode CurrentMode = GameMode.GOD;

}

但是当我定义一个 switch 语句时，它给我一个错误：

    void OnGame(){
        switch (CurrentMode){
            case GameMode.GOD: // case expressions must be constant expressionsJava(536871065)
                System.out.println("Player On God Mode");
                break;
            case GameMode.SURVIVAL: // case expressions must be constant expressionsJava(536871065)
                System.out.println("Player On Survival Mode");
                break;
            case GameMode.ADVENTURE: // case expressions must be constant expressionsJava(536871065)
                System.out.println("Player On Adventure Mode");
                break;


        }
    }

这让我很困惑。 SURVIVAL、ADVENTURE、GOD模式都是常量，我在前面加了“final”，为什么不能在switch语句中使用呢？

这是一些图片：

Answer 1

根据 Java Language Specification (JLS):

A case label has one or more case constants. Every case constant must be either a constant expression (§15.29) or the name of an enum constant (§8.9.1), or a compile-time error occurs.

你的情况显然不是 enum constant，所以我猜你正在尝试使用 constant expression 但你的 GameMode class 不符合 constant expression.

A constant expression is an expression denoting a value of primitive type or a String that does not complete abruptly and is composed using only the following...

为什么我不能将其他 class 的常量添加到 java 的 switch 语句中？

Why can't I add constant of other class into a switch statement in java?

java

constants

switch-statement