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Once the early-adopter seats are all used, the price will go up and stay at $33/year.

Partner – Microsoft – NPI EA (cat = Baeldung)
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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.

Partner – Microsoft – NPI EA (cat= Spring Boot)
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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.

Partner – Orkes – NPI EA (cat=Spring)
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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.

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Partner – Orkes – NPI EA (tag=Microservices)
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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.

eBook – Guide Spring Cloud – NPI EA (cat=Spring Cloud)
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eBook – Mockito – NPI EA (tag = Mockito)
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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.

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eBook – Java Concurrency – NPI EA (cat=Java Concurrency)
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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.

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eBook – Reactive – NPI EA (cat=Reactive)
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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:

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eBook – Java Streams – NPI EA (cat=Java Streams)
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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:

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eBook – Jackson – NPI EA (cat=Jackson)
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Building a REST API with Spring?

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Course – LS – NPI EA (cat=Jackson)
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Explore Spring Boot 3 and Spring 6 in-depth through building a full REST API with the framework:

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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:

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Course – All Access – NPI EA (cat= Spring)
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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.

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Course – LSD – NPI EA (tag=Spring Data JPA)
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Spring Data JPA is a great way to handle the complexity of JPA with the powerful simplicity of Spring Boot.

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Partner – LambdaTest – NPI EA (cat=Testing)
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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:

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Course – Spring Sale 2025 – NPI EA (cat= Baeldung)
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1. Introduction

Varargs were introduced in Java 5 and provide a short-hand for methods that support an arbitrary number of parameters of one type.

In this article, we’ll see how we can use this core Java feature.

2. Before Varargs

Before Java 5, whenever we wanted to pass an arbitrary number of arguments, we had to pass all arguments in an array or implement N methods (one for each additional parameter):

public String format() { ... }

public String format(String value) { ... }

public String format(String val1, String val2) { ... }

3. Use of Varargs

Varargs help us avoid writing boilerplate code by introducing the new syntax that can handle an arbitrary number of parameters automatically – using an array under the hood.

We can define them using a standard type declaration, followed by an ellipsis:

public String formatWithVarArgs(String... values) {
    // ...
}

And now, we can call our method with an arbitrary number of arguments, like:

formatWithVarArgs();

formatWithVarArgs("a", "b", "c", "d");

As mentioned earlier, varargs are arrays so we need to work with them just like we’d work with a normal array.

4. Rules

Varargs are straightforward to use. But there’re a few rules we have to keep in mind:

  • Each method can only have one varargs parameter
  • The varargs argument must be the last parameter

5. Heap Pollution

Using varargs can lead to so-called Heap PollutionTo better understand the heap pollution, consider this varargs method:

static String firstOfFirst(List<String>... strings) {
    List<Integer> ints = Collections.singletonList(42);
    Object[] objects = strings;
    objects[0] = ints; // Heap pollution

    return strings[0].get(0); // ClassCastException
}

If we call this strange method in a test:

String one = firstOfFirst(Arrays.asList("one", "two"), Collections.emptyList());

assertEquals("one", one);

We would get a ClassCastException even though we didn’t even use any explicit type casts here:

java.lang.ClassCastException: class java.lang.Integer cannot be cast to class java.lang.String

5.1. Safe Usage

Every time we use varargs, the Java compiler creates an array to hold the given parameters. In this case, the compiler creates an array with generic type components to hold the arguments.

When we use varargs with generic types, as there’s a potential risk of a fatal runtime exception, the Java compiler warns us about a possible unsafe varargs usage:

warning: [varargs] Possible heap pollution from parameterized vararg type T

The varargs usage is safe if and only if:

  • We don’t store anything in the implicitly created array. In this example, we did store a List<Integer> in that array
  • We don’t let a reference to the generated array escape the method (more on this later)

If we are sure that the method itself does safely use the varargs, we can use @SafeVarargs to suppress the warning.

Put simply, the varargs usage is safe if we use them to transfer a variable number of arguments from the caller to the method and nothing more!

5.2. Escaping Varargs Reference

Let’s consider another unsafe usage of varargs:

static <T> T[] toArray(T... arguments) {
    return arguments;
}

At first, it might seem that the toArray method is completely harmless. However, because it let the varargs array escape to the caller, it violates the second rule of safe varargs.

To see how this method can be dangerous, let’s use it in another method:

static <T> T[] returnAsIs(T a, T b) {
    return toArray(a, b);
}

Then if we call this method:

String[] args = returnAsIs("One", "Two");

We would, again, get a ClassCastException. Here’s what happens when we call the returnAsIs method:

  • To pass and to the toArray method, Java needs to create an array
  • Since the Object[] can hold items of any type, the compiler creates one
  • The toArray method returns the given Object[] to the caller
  • Since the call site expects a String[], the compiler tries to cast the Object[] to the expected String[], hence the ClassCastException

For a more detailed discussion on heap pollution, it’s highly recommended to read item 32 of Effective Java by Joshua Bloch.

6. Conclusion

Varargs can make a lot of boilerplate go away in Java.

And, thanks to their implicit autoboxing to and from Array, they play a role in future-proofing our code.

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.
Baeldung Pro – NPI EA (cat = Baeldung)
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Baeldung Pro comes with both absolutely No-Ads as well as finally with Dark Mode, for a clean learning experience:

>> Explore a clean Baeldung

Once the early-adopter seats are all used, the price will go up and stay at $33/year.

Partner – Microsoft – NPI EA (cat = Spring Boot)
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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.

Partner – Orkes – NPI EA (cat = Spring)
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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.

Partner – Orkes – NPI EA (tag = Microservices)
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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.

eBook – HTTP Client – NPI EA (cat=HTTP Client-Side)
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The Apache HTTP Client is a very robust library, suitable for both simple and advanced use cases when testing HTTP endpoints. Check out our guide covering basic request and response handling, as well as security, cookies, timeouts, and more:

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eBook – Java Concurrency – NPI EA (cat=Java Concurrency)
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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:

>> Download the eBook

eBook – Java Streams – NPI EA (cat=Java Streams)
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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:

>> Join Pro and download the eBook

eBook – Persistence – NPI EA (cat=Persistence)
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Working on getting your persistence layer right with Spring?

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Course – LS – NPI EA (cat=REST)

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Get started with Spring Boot and with core Spring, through the Learn Spring course:

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Course – Spring Sale 2025 – NPI EA (cat= Baeldung)
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Course – Spring Sale 2025 – NPI (All)
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eBook Jackson – NPI EA – 3 (cat = Jackson)