Collections.binarySearch() in Java

Question

I\'m using the binarySearch() method to find the position of an element in the list. And I don\'t understand why the index is -6. I see that the element is at the position 1

Answer 1

You must either sort in ascending order (per the documentation of Collections.binarySearch), or pass the custom comparator as the third parameter.

int index = Collections.binarySearch(al, 50, Collections.reverseOrder());

Failure to do this will cause undefined results.