Remove duplicates from list of integers using Lambda expression in Java

Java Lambda Program: Exercise-7 with Solution

Write a Java program to implement a lambda expression to remove duplicates from a list of integers.

Sample Solution:

Java Code:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        // Create a list of integers with duplicates
        List<Integer> nums = Arrays.asList(1, 2, 3, 3, 4, 3, 2, 5, 6, 1, 7, 7, 8, 10);
        // Print the list
        System.out.println("List elements " + nums);     
        // Remove duplicates using lambda expression
        List<Integer> unique_nums = new ArrayList<>();

        // Print the list without duplicates
        System.out.println("\nList elements without duplicates: " + unique_nums);

Sample Output:

List elements [1, 2, 3, 3, 4, 3, 2, 5, 6, 1, 7, 7, 8, 10]

List elements without duplicates: [1, 2, 3, 4, 5, 6, 7, 8, 10]


In the above exercise we use the stream() method on the nums list to convert it into a stream. We call the distinct() method to filter out duplicate elements. The distinct() method ensures that only distinct elements are retained in the stream.

Finally, we use the forEach() method and a lambda expression unique_nums::add to add each unique element to the unique_nums list.


Flowchart: Java  Exercises: Check if string is empt.

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Java: Tips of the Day

Hashset vs Treeset:

HashSet is much faster than TreeSet (constant-time versus log-time for most operations like add, remove and contains) but offers no ordering guarantees like TreeSet.


  • the class offers constant time performance for the basic operations (add, remove, contains and size).
  • it does not guarantee that the order of elements will remain constant over time
  • iteration performance depends on the initial capacity and the load factor of the HashSet.
  • It's quite safe to accept default load factor but you may want to specify an initial capacity that's about twice the size to which you expect the set to grow.


  • guarantees log(n) time cost for the basic operations (add, remove and contains)
  • guarantees that elements of set will be sorted (ascending, natural, or the one specified by you via its constructor) (implements SortedSet)
  • doesn't offer any tuning parameters for iteration performance
  • offers a few handy methods to deal with the ordered set like first(), last(), headSet(), and tailSet() etc

Important points:

  • Both guarantee duplicate-free collection of elements
  • It is generally faster to add elements to the HashSet and then convert the collection to a TreeSet for a duplicate-free sorted traversal.
  • None of these implementations are synchronized. That is if multiple threads access a set concurrently, and at least one of the threads modifies the set, it must be synchronized externally.
  • LinkedHashSet is in some sense intermediate between HashSet and TreeSet. Implemented as a hash table with a linked list running through it, however,it provides insertion-ordered iteration which is not same as sorted traversal guaranteed by TreeSet.

So a choice of usage depends entirely on your needs but I feel that even if you need an ordered collection then you should still prefer HashSet to create the Set and then convert it into TreeSet.

  • e.g. SortedSet<String> s = new TreeSet<String>(hashSet);

Ref: https://bit.ly/3d3waGh


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