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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.
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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.
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:
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:
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.
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.
Yes, we're now running our Black Friday Sale. All Access and Pro are 33% off until 2nd December, 2025:
1. Overview
In this tutorial, we’ll see why we’d use a private constructor for a class in Java and how to use it.
2. Why Use a Private Constructor?
In Java, we can declare a constructor as private using the private access specifier. If a constructor is declared private, we can’t create an object of the class, except within the class.
A private constructor is used when we want to limit the way objects of a class are instantiated. For example, we might do this if we want to create an object by only using a factory class that can create those objects. Or another situation is when we want to have only one object instance of that class.
Some of the most used cases of a private constructor are Singleton, Builder, and Factory, the creational design patterns.
Now, we can imagine any combination of these patterns as they can blend nicely and achieve a robust codebase.
3. Accessing the Private Constructor
Usually, in order to call the private constructor, the use cases listed above have other public methods that would call the private constructor within the class.
Alternatively, we can use the Java Reflection API to directly access the private constructor.
The Java Reflection API is an advanced feature that allows programs to examine and modify the runtime behavior of the application running within the JVM. Because of this, using this method isn’t recommended as it can lead to difficulty spotting and fixing bugs.
Using Reflection, we can see the methods and attributes of any class and modify or access them bypassing the access modifiers.
The most used case for using reflection is unit testing a class that has private methods. To unit test a private constructor or method using reflection, we’d need to do the following steps:
- get the class object for the class that we want to instantiate
- with the class object, call the getDeclaredContructor() method to get the Constructor object
- on the Constructor object, call the setAccessible() method and make the constructor accessible
- after the Constructor object is accessible, we can call the newInstance() method that will create a new object of that class
Let’s create a class with a private constructor. Then we’ll use the Java Reflection API to instantiate it and make sure that the private constructor was called:
private PrivateConstructorClass() {
System.out.println("Used the private constructor!");
}Let’s add a unit test where we instantiate this class using the private constructor:
@Test
public void whenConstructorIsPrivate_thenInstanceSuccess() throws Exception {
Constructor<PrivateConstructorClass> pcc = PrivateConstructorClass.class.getDeclaredConstructor();
pcc.setAccessible(true);
PrivateConstructorClass privateConstructorInstance = pcc.newInstance();
Assertions.assertTrue(privateConstructorInstance instanceof PrivateConstructorClass);
}In the console output, we should see that the private constructor was called and the print inside the constructor displayed the message. In spite of the private access modifier, we can now call the private constructor and instantiate new objects.
4. Conclusion
In this article, we saw why we’d use a private constructor and a few different ways to use it. We also learned that we can create public methods to access a private constructor or use the advanced Java Reflection API for a more advanced approach.
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.
