Baeldung Pro comes with both absolutely No-Ads as well as finally with Dark Mode, for a clean learning experience:
Once the early-adopter seats are all used, the price will go up and stay at $33/year.
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.
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, 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.
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.
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:
All Access is finally out, with all of my Spring courses. Learn JUnit is out as well, and Learn Maven is coming fast. And, of course, quite a bit more affordable. Finally.
>> GET THE COURSE
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:
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:
Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:
Yes, we're now running our Spring Sale. All Courses are 25% off until 26th May, 2025:
1. Overview
In this quick article, we’ll be looking at the CopyOnWriteArrayList from the java.util.concurrent package.
This is a very useful construct in the multi-threaded programs – when we want to iterate over a list in a thread-safe way without an explicit synchronization.
2. CopyOnWriteArrayList API
The design of the CopyOnWriteArrayList uses an interesting technique to make it thread-safe without a need for synchronization. When we are using any of the modify methods – such as add() or remove() – the whole content of the CopyOnWriteArrayList is copied into the new internal copy.
Due to this simple fact, we can iterate over the list in a safe way, even when concurrent modification is happening.
When we’re calling the iterator() method on the CopyOnWriteArrayList, we get back an Iterator backed up by the immutable snapshot of the content of the CopyOnWriteArrayList.
Its content is an exact copy of data that is inside an ArrayList from the time when the Iterator was created. Even if in the meantime some other thread adds or removes an element from the list, that modification is making a fresh copy of the data that will be used in any further data lookup from that list.
The characteristics of this data structure make it particularly useful in cases when we are iterating over it more often than we are modifying it. If adding elements is a common operation in our scenario, then CopyOnWriteArrayList won’t be a good choice – because the additional copies will definitely lead to sub-par performance.
3. Iterating Over CopyOnWriteArrayList While Inserting
Let’s say that we’re creating an instance of the CopyOnWriteArrayList that stores integers:
CopyOnWriteArrayList<Integer> numbers
= new CopyOnWriteArrayList<>(new Integer[]{1, 3, 5, 8});Next, we want to iterate over that array, so we are creating an Iterator instance:
Iterator<Integer> iterator = numbers.iterator();After the Iterator is created, we are adding a new element to the numbers list:
numbers.add(10);Keep in mind that, when we create an iterator for the CopyOnWriteArrayList, we get an immutable snapshot of the data in the list at the time iterator() was called.
Because of that, while iterating over it, we won’t see the number 10 in the iteration:
List<Integer> result = new LinkedList<>();
iterator.forEachRemaining(result::add);
assertThat(result).containsOnly(1, 3, 5, 8);Subsequent iteration using newly created Iterator will also return the number 10 that was added:
Iterator<Integer> iterator2 = numbers.iterator();
List<Integer> result2 = new LinkedList<>();
iterator2.forEachRemaining(result2::add);
assertThat(result2).containsOnly(1, 3, 5, 8, 10);4. Removing While Iterating Is Not Allowed
The CopyOnWriteArrayList was created to allow for the possibility of safe iterating over elements even when the underlying list gets modified.
Because of the copying mechanism, the remove() operation on the returned Iterator is not permitted – resulting with UnsupportedOperationException:
@Test(expected = UnsupportedOperationException.class)
public void whenIterateOverItAndTryToRemoveElement_thenShouldThrowException() {
CopyOnWriteArrayList<Integer> numbers
= new CopyOnWriteArrayList<>(new Integer[]{1, 3, 5, 8});
Iterator<Integer> iterator = numbers.iterator();
while (iterator.hasNext()) {
iterator.remove();
}
}5. Conclusion
In this quick tutorial, we had a look at the CopyOnWriteArrayList implementation from the java.util.concurrent package.
We saw the interesting semantics of this list and how it can be iterated in a thread-safe way, while other threads can continue inserting or removing elements from it.
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.
