Oracle JDK 21 Installation in KDE Neon – Step-by-step

How to Install

2. 2. Downloading Oracle JDK 21

   Download Oracle JDK 21 GNU/Linux Package

   Oracle JDK 21 .deb 64-bit

   Downloading Oracle JDK 21 for GNU/Linux Systems.

3. 3. Installing Oracle JDK 21

   Then to Setup Oracle JDK 21 on KDE Neon Linux
   First, Access the Target, usually in the Downloads folder:
   (But if downloaded with Firefox it can be instead into /tmp/mozilla*)

   cd && cd Downloads

   Now to Confirm the Package is there do:

   ls . | grep jdk

   But if you are in Trouble to Find it out on Terminal then See: How to Access Downloads Folder from Browser.

   Finally, to Install JDK 21 simply:

   sudo dpkg -i jdk-21*.deb

4. 4. Setting Up Java

   Next to Set Up Oracle Java JDK 21
   You can directly Copy & Paste the Commands into Terminal..

   sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk-21*/bin/java 1165

   sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk-21*/bin/javac 1165

   sudo update-alternatives --install /usr/bin/jar jar /usr/lib/jvm/jdk-21*/bin/jar 1165

   sudo update-alternatives --install /usr/bin/javaws javaws /usr/lib/jvm/jdk-21*/bin/javaws 1165

   Checking or Setting the System Java Version in Use with

   sudo update-alternatives --config java

   And for the Java Compiler instead:

   sudo update-alternatives --config javac

   To Switch of Java Version Just Enter the Selection Number on First, Column. :)

   

5. 5. Setting Up Env

   (Optional) Setting JAVA_HOME User Environment Variable
   And Edit the Bash environment Configuration file

   nano $HOME/.bashrc

   Append:

   export JAVA_HOME=/usr/lib/jvm/jdk-21[Release]

   Replace [Release] with the actual one on the above Command.
   Possibly to Check the JDK 21 exact PATH use in another window:

   ls /usr/lib/jvm/

   Ctr+x to Save & Exit from nano Editor :)
   Next to Load the New Bash Environment:

   bash

6. Finally, Test New Java JDK 21 Installation

   java -version