switch 语句中的最终变量大小写

2022-01-19 00:00:00 switch-statement case java final 
        final int a = 1;
        final int b;
        b = 2;
        final int x = 0;

        switch (x) {
            case a:break;     // ok
            case b:break;     // compiler error: Constant expression required

        }
        /* COMPILER RESULT:
                constant expression required
                case b:break;
                     ^
                1 error
        */

为什么会出现这种错误?如果我做了 final int b = 2，一切正常.

Why am I getting this sort of error? If I would have done final int b = 2, everything works.

推荐答案

b 可能没有被初始化，可能被分配了多个值.在您的示例中，它显然已初始化，但编译器可能不知道(而且它不能).想象一下:

b may not have been initialized and it is possible to be assigned multiple values. In your example it is obviously initialized, but probably the compiler doesn't get to know that (and it can't). Imagine:

final int b;
if (something) {
   b = 1;
} else {
   b = 2;
}

编译器在switch中需要一个常量，但是b的值取决于一些外部变量.

The compiler needs a constant in the switch, but the value of b depends on some external variable.

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