How to sort an ArrayList?

Question

I have a List of doubles in java and I want to sort ArrayList in descending order.

Input ArrayList is as below:

List testList = new Arr         


        

Answer 1

Collections.sort allows you to pass an instance of a Comparator which defines the sorting logic. So instead of sorting the list in natural order and then reversing it, one can simply pass Collections.reverseOrder() to sort in order to sort the list in reverse order:

// import java.util.Collections;
Collections.sort(testList, Collections.reverseOrder());

As mentioned by @Marco13, apart from being more idiomatic (and possibly more efficient), using the reverse order comparator makes sure that the sort is stable (meaning that the order of elements will not be changed when they are equal according to the comparator, whereas reversing will change the order)