How to Run Multiple Java Versions Concurrently on Windows

Summary: Learn how to run multiple Java versions concurrently on a Windows operating system, ensuring compatibility and flexibility for different applications and development environments.
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How to Run Multiple Java Versions Concurrently on Windows

Managing multiple Java versions on a single machine can be challenging but is often necessary for various development environments or compatibility purposes. Fortunately, Windows provides several methods to run different Java versions concurrently, allowing developers to switch between them as needed. In this guide, we'll explore effective ways to manage and use multiple Java installations on a Windows operating system.

Installing Multiple Java Versions

First, ensure you have the necessary Java Development Kits (JDKs) downloaded and installed on your machine. You can install different versions of JDK from the official Oracle website, OpenJDK, or other reliable sources.

Download the JDK versions you need.

Install each JDK to separate directories, for example:

C:\Java\jdk1.8.0_281

C:\Java\jdk-11.0.10

C:\Java\jdk-15.0.2

Managing PATH Variables

By default, the PATH environment variable determines which Java version is used globally. To enable concurrent running of multiple Java versions, you'll need to manage the PATH and JAVA_HOME variables carefully.

Setting JAVA_HOME

The JAVA_HOME environment variable needs to point to the required version of Java for your current task. You can set this variable dynamically using the Command Prompt or via the Windows System Properties.

Via Command Prompt:

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This sets JAVA_HOME to Java 8 and updates the PATH for the current session.

Via System Properties:

Go to System Properties > Advanced > Environment Variables.

Click New to add a new variable or Edit to change the existing JAVA_HOME.

Set JAVA_HOME to the path of your preferred JDK.

After setting the JAVA_HOME, ensure the PATH variable includes %JAVA_HOME%\bin at the start.

Using Scripts to Switch Versions

To make switching between Java versions easier, especially for different projects, you can create batch scripts that automate the process.

Create a batch file for each required Java version, for instance:

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Run the desired batch file to quickly switch Java versions for your development environment.

Using Tools for Version Management

Tools like SDKMAN! can simplify managing multiple Java versions on Windows, although they are more commonly used on Unix-like systems. For Windows, it's done somewhat manually or with the help of specialized scripts and tools, saving effort over time.

Verifying the Current Java Version

To ensure you're using the correct Java version, you can check the active version via the Command Prompt:

[[See Video to Reveal this Text or Code Snippet]]

This command will display the current version of Java configured in PATH.

Conclusion

Running multiple Java versions concurrently on Windows is achievable with careful management of environment variables and leveraging simple scripts. By setting up different JDK installations and using dynamic configuration, you can switch between versions seamlessly, ensuring a flexible development environment. This approach helps maintain compatibility across projects that require different Java versions.