How to Install Oracle JDK 13 on Lubuntu 20.04 Focal LTS Gnu/Linux

Switching System Java

4. 4. Setting Up Java

   Next to Set Up Oracle Java JDK 13
   You can directly Copy & Paste the Commands into Terminal..

   sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk-13*/bin/java 1165

   sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk-13*/bin/javac 1165

   sudo update-alternatives --install /usr/bin/jar jar /usr/lib/jvm/jdk-13*/bin/jar 1165

   sudo update-alternatives --install /usr/bin/javaws javaws /usr/lib/jvm/jdk-13*/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-13[Release]

   Replace [Release] with the actual one on the above Command.
   Possibly to Check the JDK 13 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 13 Installation.

   java -version