[hardwired]

According to this test/exploration your code should work. I wonder if the variable input could be something other than a char.

Code:

public class Test {
    public static void main(String[] args) {
        char[] chars = { 'a', 'b', 'c', 'd' };
        explore(chars);
        String s = "";
        for(int j = 0; j < chars.length; j++) {
            char c = chars[j];
            switch(c) {
                case 'a':     // both seem to
//                case 97:    // work okay
                    s = "a";
                    break;
                case 'b':
//                case 98:
                   s = "b";
                   break;
                case 'c':
//                case 99:
                   s = "c";
                   break;
                case 'd':
//                case 100:
                   s = "d";
                   break;
                default:
                   s = "default";
            }
            System.out.printf("j = %d  s = %s%n", j, s);
        }
    }

    private static void explore(char[] chars) {
        for(int j = 0; j < chars.length; j++) {
            char c = chars[j];
            int n = (int)chars[j];
            System.out.printf("j = %d  c = %s  n = %3d  c == n = %b%n",
                               j, c, n, c == n);
        }
    }
}