Finding the Differences Between Two Lists in Java

Last updated: April 4, 2025

Written by: Daniel Strmecki

Reviewed by: Ashley Frieze

Java List

Azure Container Apps is a fully managed serverless container service that enables you to build and deploy modern, cloud-native Java applications and microservices at scale. It offers a simplified developer experience while providing the flexibility and portability of containers.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, you can get started over on the documentation page.

And, you can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Modern software architecture is often broken. Slow delivery leads to missed opportunities, innovation is stalled due to architectural complexities, and engineering resources are exceedingly expensive.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

With Orkes Conductor managed through Orkes Cloud, developers can focus on building mission critical applications without worrying about infrastructure maintenance to meet goals and, simply put, taking new products live faster and reducing total cost of ownership.

Try a 14-Day Free Trial of Orkes Conductor today.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

Try a 14-Day Free Trial of Orkes Conductor today.

End-to-end testing is a very useful method to make sure that your application works as intended. This highlights issues in the overall functionality of the software, that the unit and integration test stages may miss.

Playwright is an easy-to-use, but powerful tool that automates end-to-end testing, and supports all modern browsers and platforms.

When coupled with LambdaTest (an AI-powered cloud-based test execution platform) it can be further scaled to run the Playwright scripts in parallel across 3000+ browser and device combinations:

>> Automated End-to-End Testing With Playwright

1. Overview

Finding differences between collections of objects of the same data type is a common programming task. As an example, imagine we have a list of students who applied for an exam, and another list of students who passed it. The difference between those two lists would give us the students who didn’t pass the exam.

In Java, there’s no explicit way of finding the differences between two lists in the List API, though there are some helper methods that come close.

In this quick tutorial, we’ll learn how to find the differences between the two lists. We’ll try a few different approaches, including plain Java (with and without Streams), and third-party libraries, such as Guava and the Apache Commons Collections.

2. Test Setup

Let’s start by defining two lists, which we’ll use to test out our examples:

public class FindDifferencesBetweenListsUnitTest {

    private static final List listOne = Arrays.asList("Jack", "Tom", "Sam", "John", "James", "Jack");
    private static final List listTwo = Arrays.asList("Jack", "Daniel", "Sam", "Alan", "James", "George");

}

3. Using the Java List API

We can create a copy of one list and then remove all the elements common with the other using the List method removeAll():

List<String> differences = new ArrayList<>(listOne);
differences.removeAll(listTwo);
assertEquals(2, differences.size());
assertThat(differences).containsExactly("Tom", "John");

Let’s reverse this to find the differences the other way around:

List<String> differences = new ArrayList<>(listTwo);
differences.removeAll(listOne);
assertEquals(3, differences.size());
assertThat(differences).containsExactly("Daniel", "Alan", "George");

We should also note that if we want to find the common elements between the two lists, List also contains a retainAll method.

4. Using the Streams API

A Java Stream can be used for performing sequential operations on data from collections, which includes filtering the differences between lists:

List<String> differences = listOne.stream()
            .filter(element -> !listTwo.contains(element))
            .collect(Collectors.toList());
assertEquals(2, differences.size());
assertThat(differences).containsExactly("Tom", "John");

As in our first example, we can switch the order of lists to find the different elements from the second list:

List<String> differences = listTwo.stream()
            .filter(element -> !listOne.contains(element))
            .collect(Collectors.toList());
assertEquals(3, differences.size());
assertThat(differences).containsExactly("Daniel", "Alan", "George");

We should note that the repeated calling of List.contains() can be a costly operation for larger lists.

5. Using Third-Party Libraries

5.1. Using Google Guava

Guava contains a handy Sets.difference method, but to use it, we need to first convert our List to a Set:

List<String> differences = new ArrayList<>(Sets.difference(Sets.newHashSet(listOne), Sets.newHashSet(listTwo)));
assertEquals(2, differences.size());
assertThat(differences).containsExactlyInAnyOrder("Tom", "John");

We should note that converting the List to a Set will have the effect of duplicating and reordering it.

5.2. Using Apache Commons Collections

The CollectionUtils class from Apache Commons Collections contains a removeAll method.

This method does the same as List.removeAll, while also creating a new collection for the result:

List<String> differences = new ArrayList<>((CollectionUtils.removeAll(listOne, listTwo)));
assertEquals(2, differences.size());
assertThat(differences).containsExactly("Tom", "John");

6. Handling Duplicate Values

Now let’s look at finding the differences when two lists contain duplicated values.

To achieve this, we need to remove the duplicate elements from the first list, precisely as many times as they are contained in the second list.

In our example, the value “Jack” appears twice in the first list, and only once in the second list:

List<String> differences = new ArrayList<>(listOne);
listTwo.forEach(differences::remove);
assertThat(differences).containsExactly("Tom", "John", "Jack");

We can also achieve this using the subtract method from Apache Commons Collections:

List<String> differences = new ArrayList<>(CollectionUtils.subtract(listOne, listTwo));
assertEquals(3, differences.size());
assertThat(differences).containsExactly("Tom", "John", "Jack");

7. Conclusion

In this article, we explored a few ways to find the differences between lists. We covered a basic Java solution, a solution using the Streams API, and solutions using third-party libraries, like Google Guava and Apache Commons Collections.

We also discussed how to handle duplicate values.

The code backing this article is available on GitHub. Once you're logged in as a Baeldung Pro Member, start learning and coding on the project.

Of course, Azure Container Apps has really solid support for our ecosystem, from a number of build options, managed Java components, native metrics, dynamic logger, and quite a bit more.

To learn more about Java features on Azure Container Apps, visit the documentation page.

You can also ask questions and leave feedback on the Azure Container Apps GitHub page.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

Try a 14-Day Free Trial of Orkes Conductor today.

Orkes is the leading workflow orchestration platform built to enable teams to transform the way they develop, connect, and deploy applications, microservices, AI agents, and more.

Try a 14-Day Free Trial of Orkes Conductor today.