java - final variable case in switch statement

Question

        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
        */

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

Answer 1

The case in the switch statements should be constants at compile time. The command

final int b=2

assigns the value of 2 to b, right at the compile time. But the following command assigns the value of 2 to b at Runtime.

final int b;
b = 2;

Thus, the compiler complains, when it can't find a constant in one of the cases of the switch statement.