Character Comparison

    public static void main(String [] args) throws InterruptedException {
        System.out.println("a-z: "+('a'-'z'));
        System.out.println("a-A: "+('a'-'A'));
        System.out.println("a-Z: "+('a'-'Z'));
        System.out.println("A-Z: "+('A'-'Z'));
        System.out.println("A-9: "+('A'-'9'));
        System.out.println("a-0: "+('a'-'0'));
        System.out.println("z-0: "+('z'-'0'));
        System.out.println("z-A: "+('z'-'A'));
        System.out.println("z-Z: "+('z'-'Z'));
        System.out.println("A-0: "+('A'-'0'));
        System.out.println("Z-0: "+('Z'-'0'));
    }

Output

a-z: -25
a-A: 32
a-Z: 7
A-Z: -25
A-9: 8
a-0: 49
z-0: 74
z-A: 57
z-Z: 32
A-0: 17
Z-0: 42

So the summary is:

0 < 9 < A < Z < a < z