How to Install OpenJDK 21 on Ubuntu 24.04

Install OpenJDK 21

You can install OpenJDK 21 on Ubuntu 24.04 using your terminal. This command downloads the latest Java Development Kit from Ubuntu’s official software sources. Running the update and install commands is all you need to do to get OpenJDK 21 ready on your computer.

To install OpenJDK 21, run the command below.

sudo apt update
sudo apt install openjdk-21-jdk

sudo tee -a /etc/profile.d/java.sh <<'EOF'
export JAVA_HOME=$(dirname $(dirname $(readlink $(readlink $(which java)))))
export PATH=$PATH:$JAVA_HOME/bin
EOF

Activate the script by running the command below.

sudo -s
source /etc/profile.d/java.sh

Test OpenJDK

After you install OpenJDK 21, it’s a good idea to test it to make sure everything is working correctly. Open your terminal and type `java –version`. This command will show you the details of your installed Java version, confirming that OpenJDK 21 is now properly set up on your Ubuntu system.

java --version

It should output similar lines shown below.

openjdk 21.0.6 2025-01-21
OpenJDK Runtime Environment (build 21.0.6+7-Ubuntu-124.04.1)
OpenJDK 64-Bit Server VM (build 21.0.6+7-Ubuntu-124.04.1, mixed mode, sharing)

OpenJDK is installed and ready to use.

Choose the default

If you have more than one Java version on your Ubuntu computer, you can easily choose which one to use as the default. By running the command `sudo update-alternatives –config java` in your terminal, you can manage and switch between your installed Java versions, controlling which one applications will use automatically.

sudo update-alternatives --config java

Select the Java version you wish to use as the default.

  Selection    Path                                         Priority   Status
------------------------------------------------------------
* 0            /usr/lib/jvm/java-21-openjdk-amd64/bin/java   2111      auto mode
  1            /usr/lib/jvm/java-17-openjdk-amd64/bin/java   1711      manual mode
  2            /usr/lib/jvm/java-21-openjdk-amd64/bin/java   2111      manual mode

Press <enter> to keep the current choice[*], or type selection number: 

sudo update-alternatives --config javac

Choose the javac version you want to set as default.

  Selection    Path                                          Priority   Status
------------------------------------------------------------
* 0            /usr/lib/jvm/java-21-openjdk-amd64/bin/javac   2111      auto mode
  1            /usr/lib/jvm/java-17-openjdk-amd64/bin/javac   1711      manual mode
  2            /usr/lib/jvm/java-21-openjdk-amd64/bin/javac   2111      manual mode

Press <enter> to keep the current choice[*], or type selection number: 

That should do it!

Conclusion:

In summary, installing OpenJDK 21 on Ubuntu 24.04 is a straightforward process that allows developers to harness the power of Java for application development. Here are the key takeaways:

• OpenJDK 21 provides a comprehensive set of tools necessary for Java development, including the Java compiler and runtime.
• The installation involves simple commands executed through the terminal, utilizing Ubuntu’s default repositories.
• Configuring the JAVA_HOME variable and updating the environment PATH ensures proper functionality of the OpenJDK installation.
• You can verify the installation with the java --version command to ensure everything is set up correctly.
• Managing multiple OpenJDK versions is seamless using the update-alternatives command, allowing for flexibility in development environments.

Following these steps, you can effectively set up and manage OpenJDK on your Ubuntu system, which is ready for your Java development needs.