Mocking is an essential part of unit testing, and the Mockito library makes it easy to write clean and intuitive unit tests for your Java code.
Get started with mocking and improve your application tests using our Mockito guide:
Handling concurrency in an application can be a tricky process with many potential pitfalls. A solid grasp of the fundamentals will go a long way to help minimize these issues.
Get started with understanding multi-threaded applications with our Java Concurrency guide:
Spring 5 added support for reactive programming with the Spring WebFlux module, which has been improved upon ever since. Get started with the Reactor project basics and reactive programming in Spring Boot:
Since its introduction in Java 8, the Stream API has become a staple of Java development. The basic operations like iterating, filtering, mapping sequences of elements are deceptively simple to use.
But these can also be overused and fall into some common pitfalls.
To get a better understanding on how Streams work and how to combine them with other language features, check out our guide to Java Streams:
Explore Spring Boot 3 and Spring 6 in-depth through building a full REST API with the framework:
Yes, Spring Security can be complex, from the more advanced functionality within the Core to the deep OAuth support in the framework.
I built the security material as two full courses - Core and OAuth, to get practical with these more complex scenarios. We explore when and how to use each feature and code through it on the backing project.
You can explore the course here:
Spring Data JPA is a great way to handle the complexity of JPA with the powerful simplicity of Spring Boot.
Get started with Spring Data JPA through the guided reference course:
Refactor Java code safely — and automatically — with OpenRewrite.
Refactoring big codebases by hand is slow, risky, and easy to put off. That’s where OpenRewrite comes in. The open-source framework for large-scale, automated code transformations helps teams modernize safely and consistently.
Each month, the creators and maintainers of OpenRewrite at Moderne run live, hands-on training sessions — one for newcomers and one for experienced users. You’ll see how recipes work, how to apply them across projects, and how to modernize code with confidence.
Join the next session, bring your questions, and learn how to automate the kind of work that usually eats your sprint time.
Regression testing is an important step in the release process, to ensure that new code doesn't break the existing functionality. As the codebase evolves, we want to run these tests frequently to help catch any issues early on.
The best way to ensure these tests run frequently on an automated basis is, of course, to include them in the CI/CD pipeline. This way, the regression tests will execute automatically whenever we commit code to the repository.
In this tutorial, we'll see how to create regression tests using Selenium, and then include them in our pipeline using GitHub Actions:, to be run on the LambdaTest cloud grid:
1. Overview
In this tutorial, we’ll look at the maximum size of an array in Java.
2. Max Size
A Java program can only allocate an array up to a certain size. It generally depends on the JVM that we’re using and the platform. Since the index of the array is int, the approximate index value can be 2^31 – 1. Based on this approximation, we can say that the array can theoretically hold 2,147,483,647 elements.
For our example, we’re using the OpenJDK and Oracle implementations of Java 8 and Java 15 on Linux and Mac machines. The results were the same throughout our testing.
This can be verified using a simple example:
for (int i = 2; i >= 0; i--) {
try {
int[] arr = new int[Integer.MAX_VALUE - i];
System.out.println("Max-Size : " + arr.length);
} catch (Throwable t) {
t.printStackTrace();
}
}During the execution of the above program, using Linux and Mac machines, similar behavior is observed. On execution with VM arguments -Xms2G -Xmx2G, we’ll receive the following errors:
java.lang.OutOfMemoryError: Java heap space
at com.example.demo.ArraySizeCheck.main(ArraySizeCheck.java:8)
java.lang.OutOfMemoryError: Requested array size exceeds VM limit
at com.example.demo.ArraySizeCheck.main(ArraySizeCheck.java:8)
java.lang.OutOfMemoryError: Requested array size exceeds VM limit
Note that the first error is different from the last two. The last two errors mention the VM limitation, whereas the first one is about heap memory limitation.
Now let’s try with the VM arguments -Xms9G -Xmx9G to receive the exact maximum size:
Max-Size: 2147483645
java.lang.OutOfMemoryError: Requested array size exceeds VM limit
at com.example.demo.ArraySizeCheck.main(ArraySizeCheck.java:8)
java.lang.OutOfMemoryError: Requested array size exceeds VM limit
at com.example.demo.ArraySizeCheck.main(ArraySizeCheck.java:8)
The results show the maximum size is 2,147,483,645.
The same behavior can be observed for byte, boolean, long, and other data types in the array, and the results are the same.
3. ArraySupport
ArraysSupport is a utility class in OpenJDK, which suggests having the maximum size as Integer.MAX_VALUE – 8 to make it work with all the JDK versions and implementations.
4. Conclusion
In this article, we looked at the maximum size of an array in Java.
