Solved: How do I install and use multiple JDKs on Windows

Key Takeaways

• The article explains how to install and use multiple JDKs on Windows, including Oracle JDK and OpenJDK, and how to switch between them easily using a command-line tool called jEnv.
• The article also explains the differences between Oracle JDK and OpenJDK, and how to check your Java version on Windows.

Problem

Java is not a static language, and it evolves over time with new features and improvements. This means that there are different versions of Java available, and sometimes you may need to use a specific version for a particular project or tool.

For example, some projects may require Java 8, while others may need Java 11 or Java 17. Some tools may work better with Oracle JDK, while others may prefer OpenJDK. How can you manage multiple JDKs on your Windows machine and switch between them easily?

In this article, we will show you how to install and use multiple JDKs on Windows, including Oracle JDK and OpenJDK, and how to switch between them easily using a command-line tool. We will also explain the differences between Oracle JDK and OpenJDK, and how to check your Java version on Windows.

Install multiple JDKs on Windows

Installing multiple JDKs on Windows is fairly easy, as you can download and run the installer for each version and implementation that you want. You can find the download links for Oracle JDK and OpenJDK below:

• Oracle JDK
• OpenJDK

When you install a JDK, it will create a folder in your Program Files directory, such as C:\Program Files\Java\jdk-17. You can choose a different location if you prefer, but make sure to remember it for later use.

You can install as many JDKs as you want, as long as they are in separate folders. However, you need to configure your environment variables to tell your system which JDK to use by default.

Solution: Install and use multiple JDKs on Windows

Step 1: Configure environment variables for JDK

Environment variables are settings that affect how your system and applications behave. There are two types of environment variables: user variables and system variables. User variables apply only to the current user account, while system variables apply to all users and processes on the system.

To configure environment variables for JDK, you need to set two variables: JAVA_HOME and PATH. JAVA_HOME is the variable that points to the location of your JDK installation, and PATH is the variable that contains the directories where your system looks for executable files.

To set these variables, follow these steps:

1. Open the Start menu and search for “environment variables”. Click on “Edit the system environment variables”.
2. In the System Properties window, click on the “Environment Variables” button.
3. In the Environment Variables window, under the User variables section, click on the “New” button.
4. In the New User Variable window, enter “JAVA_HOME” as the variable name, and the path to your JDK installation as the variable value. For example, if you installed JDK 17 in the default location, enter “C:\Program Files\Java\jdk-17”. Click on “OK”.
5. In the Environment Variables window, under the User variables section, select the “Path” variable and click on the “Edit” button.
6. In the Edit Environment Variable window, click on the “New” button and enter “%JAVA_HOME%\bin” as the new entry. This will add the bin directory of your JDK to the PATH variable. Click on “OK”.
7. In the Environment Variables window, click on “OK” to save the changes and close the window.
8. In the System Properties window, click on “OK” to close the window.

You have now set the environment variables for JDK. However, these changes will only take effect in new command prompt windows, not the existing ones. You can also change the JAVA_HOME and PATH variables for the system variables section if you want to apply them to all users and processes on the system.

Step 2: Switch between multiple JDKs on Windows

If you have installed multiple JDKs on Windows, you may want to switch between them for different projects or tools. There are several ways to do this, but one of the easiest and fastest ways is to use a command-line tool called jEnv.

jEnv is a tool that allows you to manage multiple Java environments on Windows. It lets you add, remove, list, and switch between different JDKs with simple commands. You can also set a global, local, or shell JDK version, and create aliases for different JDKs.

To use jEnv, you need to download and install it from its official website. You can also find the documentation and usage examples there. Here are some basic commands to get you started:

• To add a JDK to jEnv, use the command jenv add <name> <path>, where <name> is a custom name for the JDK, and <path> is the path to the JDK installation. For example, to add JDK 17, use jenv add jdk17 C:\Program Files\Java\jdk-17.
• To list all the JDKs managed by jEnv, use the command jenv versions.
• To switch to a JDK globally, use the command jenv global <name>, where <name> is the name of the JDK. For example, to switch to JDK 17 globally, use jenv global jdk17.
• To switch to a JDK locally, use the command jenv local <name>, where <name> is the name of the JDK. This will create a .java-version file in the current directory, and jEnv will use the JDK specified in that file for that directory and its subdirectories. For example, to switch to JDK 17 locally, use jenv local jdk17.
• To switch to a JDK for the current shell session, use the command jenv shell <name>, where <name> is the name of the JDK. This will set the JAVA_HOME and PATH variables for the current shell session only. For example, to switch to JDK 17 for the current shell session, use jenv shell jdk17.
• To create an alias for a JDK, use the command jenv alias <name> <alias>, where <name> is the name of the JDK, and <alias> is the alias name. For example, to create an alias for JDK 17 as java17, use jenv alias jdk17 java17.
• To remove a JDK from jEnv, use the command jenv remove <name>, where <name> is the name of the JDK. For example, to remove JDK 17 from jEnv, use jenv remove jdk17.

Step 3: Check Java version on Windows

To check the Java version on Windows, you can use one of the following methods:

• Use the “About Java” utility. Open the Start menu and search for “About Java”. Click on the result and you will see the Java version and build number in the first line.
• Use the “java -version” command. Open a command prompt window and type java -version. You will see the Java version and build number in the output.
• Use the “javac -version” command. Open a command prompt window and type javac -version. You will see the Java compiler version in the output.

Frequently Asked Questions (FAQs)

Question: What is JDK?

Answer: JDK stands for Java Development Kit, and it is a software development environment that contains the tools and libraries needed for developing Java applications. It includes the Java Runtime Environment (JRE), which is the component that runs Java programs, and the Java compiler, debugger, and other utilities.

There are different implementations of JDK, such as Oracle JDK, OpenJDK, IBM JDK, Azul JDK, and more. They all follow the Java specification and pass the Java Technology Certification Kit (TCK), which ensures compatibility and interoperability. However, they may have some differences in terms of performance, features, licensing, and support.

Question: What is the difference between Oracle JDK and OpenJDK?

Answer: Oracle JDK and OpenJDK are two of the most widely used JDK implementations. Oracle JDK is the official JDK from Oracle, and it is based on the OpenJDK source code. OpenJDK is an open-source project that is maintained by Oracle, Red Hat, and the community.

The main difference between Oracle JDK and OpenJDK is the licensing and support. Oracle JDK requires a commercial license for production use, and it offers long-term support (LTS) for certain versions. OpenJDK is free and open-source, and it does not offer LTS for any version.

Another difference is that Oracle JDK may have some additional features or optimizations that are not available in OpenJDK, such as Java Flight Recorder, Java Mission Control, ZGC, and GraalVM. However, these features may be added to OpenJDK in the future, as Oracle plans to converge the two JDKs.

Question: What is the difference between JDK and JRE?

Answer: JDK stands for Java Development Kit, and it is a software development environment that contains the tools and libraries needed for developing Java applications. JRE stands for Java Runtime Environment, and it is the component that runs Java programs. JDK includes JRE, but JRE does not include JDK.

Question: What is the difference between JDK and JVM?

Answer: JDK stands for Java Development Kit, and it is a software development environment that contains the tools and libraries needed for developing Java applications. JVM stands for Java Virtual Machine, and it is the component that executes Java bytecode, which is the intermediate representation of Java programs. JDK includes JVM, but JVM does not include JDK.

Question: What is the difference between Java SE and Java EE?

Answer: Java SE stands for Java Standard Edition, and it is the core Java platform that provides the basic functionality and libraries for Java applications. Java EE stands for Java Enterprise Edition, and it is an extension of Java SE that provides additional features and libraries for developing enterprise-scale, distributed, and web-based applications.

Question: What is the latest version of Java?

Answer: The latest version of Java as of November 2021 is Java 17, which is also a long-term support (LTS) version. Java 17 was released on September 14, 2021, and it introduced several new features and enhancements, such as sealed classes, pattern matching for switch expressions, text blocks, and more. You can find more details about Java 17 on its [official website].

Summary

In this article, we have learned how to install and use multiple JDKs on Windows, including Oracle JDK and OpenJDK, and how to switch between them easily using a command-line tool called jEnv. We have also explained the differences between Oracle JDK and OpenJDK, and how to check your Java version on Windows.

We hope that this article has helped you to understand and manage multiple Java environments on Windows. If you have any questions or feedback, please feel free to leave a comment below.

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