switch语句上的“需要常量表达式”？ [复制]

Question

我正在研究 switch 语句。 Java 编译器告诉我，我的案例 (x, y, z, a) 需要一个常量表达式；这是从哪里来的，为什么我的代码不能运行 switch 语句？

public class JavaPractice {
    public static void main ( String[] args ) {

        System.out.println("What's your happinessLevel? From 0 - 10");
        int _userHappinessLevel = IO.readInt();

        if ( _userHappinessLevel < 0 ) {
            x = _userHappinessLevel;
        } else if ( _userHappinessLevel <= 3) {
            y = _userHappinessLevel;
        } else if ( _userHappinessLevel > 3 && _userHappinessLevel <= 6 ) {
            z = _userHappinessLevel;
        } else if ( _userHappinessLevel > 6 && _userHappinessLevel <= 10) {
            a = _userHappinessLevel;
        } else {
            b = _userHappinessLevel;
        }


        switch (_userHappinessLevel) {

            case x:
                IO.reportBadInput();
                break;
            case y:
                System.out.println("Hope you feel better");
                break;
            case z:
                System.out.println("You're getting there");
                break;
            case a:
                System.out.println(":)");
                break;
            default:
                IO.reportBadInput();
                break;
            }

    }
}

Answer 1

因为 _userHappinessLevel 的数据类型是 int，当你把这个变量放在 switch 中时，大小写应该是数字，或者你可以使用 enum 来做一些事情，比如给字符串一个“int”名称。