Interfaces and comparables

Question

I have objects that implement an interface so certain methods are available (getTime, getValue, etc).

However I also want to force these objects to be sortable in the same way using Comparable but I can't define bodies in the interface (at least in Android Java).

What can I do?

Answer 1

You can define bodies in an interface using the default keyword (which is not part of the signature):

public interface MyInterface extends Comparable<MyInterface> {

    @Override
    default int compareTo(MyInterface other) {
        return 0;
    }

}

---

However, if you want to sort on different criteria from time to time. Passing a comparator with the sort method is a much better choice.

public interface MyInterface  {
    int getTime();
    int getValue();
}

Then call like:

List<MyInterface> list= ...;
list.sort((mi1, mi2) -> Integer.compare(mi1.getTime(), mi2.getTime())); // sorts by time
list.sort((mi1, mi2) -> Integer.compare(mi1.getValue(), mi2.getValue())); // sorts by value