How do I tell Java that an interface implements Comparable?

Question

I have an interface named IDebt, and a class implementing said interface named Debt.

I also have a list made of objects implementing the IDebt interface:

List<IDebt> debtList = new ArrayList<IDebt>();

The class Debt implements Comparable, but when I do Collections.sort(debtList) I get an error, because Java has no way to know that the object implementing IDebt as such implements Comparable.

How can I solve this?

Answer 1

You can do this:

public static interface MyInterface extends Comparable<MyInterface> {

}

public static class MyClass implements MyInterface {

    @Override
    public int compareTo(MyInterface another) {
        return 0; //write a comparison method here
    }
}

Then

List<MyInterface> test = new ArrayList<>();
Collections.sort(test);

will work

Update: also for sorting maybe this makes more sense:

Collections.sort(test, new Comparator<MyInterface >() {
        @Override
        public int compare(MyInterface lhs, MyInterface rhs) {
            return 0;
        }
    });