Question

I want to implement Comparable for one of my class.

My test-Array: A1, A2, A3, B1, B2, B3

I want so sort like this:
-sorting by letter

-if A then ascending number

-if B then descending number

Outcome expected: A1, A2, A3, B3, B2, B1

The following code would always give me letter and numbers ascending, like A1, A2, A3, B1, B2, B3.
How can I switch the order of numbers based on which letter Foo has?

class Foo implements Comparable {
    String letter, int number;

    int compareTo(Foo f) {
        int x = letter.compareTo(f.letter);
        return x != 0 ? x : number.compareTo(f.number);
    }
}

Answer 1

You could do something like this:

int compareTo(Foo f) {
    int x = letter.compareTo(f.letter);
    return x != 0 ? x 
         : letter.equals("A") ? number.compareTo(f.number)
                              : f.number.compareTo(number);
}

(That’s assuming you want to treat all non-A values as descending, of course…)