Collections.sort() in Java with Examples

The Collections.sort() method in Java is used to sort elements of a List in ascending order. It is part of the java.util.Collections class and works with List implementations like ArrayList and LinkedList. It simplifies sorting by providing a built-in mechanism.

• Sorts elements based on natural ordering or custom Comparator
• Works with List implementations, not arrays
• Modifies the list in-place without creating a new list

Syntax

Collections.sort(List<T> list);

• Sorts the list in ascending order (natural order)
• Elements must implement Comparable

Example: Sorting an ArrayList in ascending order

List after the use of Collection.sort() :
[Dear, Friends, Geeks For Geeks, Is, Superb]

• Time Complexity: O(N log N) as time complexity of Collections.sort() is O(nlog(n)).
• Auxiliary Space: O(N)  

Example: Sorting an ArrayList in descending order 

List after the use of Collection.sort() :
[Superb, Is, Geeks For Geeks, Friends, Dear]

• Time Complexity: O(N log N) as time complexity of Collections.sort() is O(nlog(n)).
• Auxiliary Space: O(N)

Custom Sorting

Sorting an ArrayList according to user defined criteria. We can use Comparator Interface for this purpose.

Syntax

Custom Sorting using Comparato

• Sorts the list using a custom sorting logic
• We define the order using a Comparator