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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.
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 learn the cause of “Could not reserve enough space for object heap” error, while going through some possible scenarios.
2. Symptoms
“Could not reserve enough space for object heap” is a specific JVM error that is raised when Java process cannot create the virtual machine due to memory constraints encountered on the running system:
java -Xms4G -Xmx4G -jar HelloWorld.jar
Error occurred during initialization of VM
Could not reserve enough space for object heap
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.Generally, there are two possible scenarios when we encounter the error.
Firstly, when we lunch a Java process with max heap size limit parameter (-Xmx) and the value is more than what the process can have on the operating system.
The heap size limit varies based on several constraints:
- hardware architecture (32/64 bit)
- JVM bit version (32/64 bit)
- the operating system that we use
Secondly, when the Java process is not able to reserve the specified amount of memory due to other applications that run on the same system and consume memory.
3. Heap Size
Java heap space is the memory allocation pool for the runtime Java program, managed by the JVM itself. By default, the allocation pool is restricted to the initial and maximum size. To learn more about Heap Space in Java, have a look at this article here.
Let’s see what the maximum heap size is in different environments and how we can set the limits.
3.1. Max Heap Size
The maximum theoretical heap limit for the 32-bit and 64-bit JVM is easy to determine by looking at the available memory space, 2^32 (4 GB) for 32-bit JVM and 2^64 (16 Exabytes) for 64-bit JVM.
In practice, due to various constraints, the limit can be much lower and varies given the operating system. For example, on 32-bit Windows systems the maximum heap size range is between 1.4 GB to 1.6 GB. In contrast, on 32-bit Linux systems, the maximum heap size can stretch up to 3 GB.
For this reason, if the application requires a large heap we should use the 64-bit JVM. However, with a large heap, the garbage collector will have more work to do, so it’s important to find a good balance between heap size and performance.
3.2. How To Control Heap Size Limits?
We have two options to control the heap size limits of a JVM.
First, by using Java command line parameters at each JVM initialization:
-Xms<size> Sets initial Java heap size. This value must be a multiple of 1024 and greater than 1 MB.
-Xmx<size> Sets maximum Java heap size. This value must be a multiple of 1024 and greater than 2 MB.
-Xmn<size> Sets the initial and maximum size (in bytes) of the heap for the young generation.For the size value, we may append letter k or K, m or M and g or G to indicate kilobytes, megabytes, and gigabytes respectively. If no letter is specified, the default unit (byte), is used.
-Xmn2g
-Xmn2048m
-Xmn2097152k
-Xmn2147483648Secondly, by using environment variable JAVA_OPTS to configure above Java command line parameters globally. Due to this, each JVM initialization on the system will automatically use the configurations set in the environment variable.
JAVA_OPTS="-Xms256m -Xmx512m"For more information, check out our comprehensive JVM Parameters guide.
4. Conclusion
In this tutorial, we discussed two possible scenarios when JVM is not able to reserve enough space for object heap. We also learned how to control the heap size limits in order to mitigate this error.
Next, learn more about potential memory issues at runtime and how to identify them.
