Java Interview Questions Comparator and Comparable

1. How do the Comparable and Comparator interfaces differ, and when should you use one over the other?

The Comparable interface is used to define a natural ordering for a class, which allows objects of that class to be sorted automatically in the default manner. The Comparator interface, on the other hand, is used to define a custom ordering for a class, which allows objects of that class to be sorted in a specific manner. You should use the Comparable interface if you want to use the default sorting behavior for a class, and you should use the Comparator interface if you want to define a custom sorting behavior for a class.

2. How to implement a custom comparator using a lambda expression?

// Define a custom comparator that sorts strings by their length,
// with the shortest strings appearing first in the sorted list.
Comparator<String> stringLengthComparator = (s1, s2) -> s1.length() - s2.length();

// Use the comparator to sort a list of strings.
List<String> stringList = Arrays.asList("abc", "def", "gh", "ijkl");
stringList.sort(stringLengthComparator);

// The sorted list should be: ["gh", "abc", "def", "ijkl"]