Download the JDK:
Oracle: https://www.oracle.com/java/technologies/downloads/
OpenJDK:https://openjdk.org/

Extract the file "jdk-23_linux-x64_bin.tar.gz" to the installation directory: /opt/jdk-23.0.2

$ sudo tar -xf jdk-23_linux-x64_bin.tar.gz -C /opt/

Change the folder permissions (replace 'mtitek' with your username):

$ sudo chmod -R 755 /opt/jdk-23.0.2
$ sudo chown -R mtitek:mtitek /opt/jdk-23.0.2

Setup the environment variables JAVA_HOME and PATH:

• Open the file "~/.profile" or "~/.bashrc" for persistent settings:
  

  $ vi ~/.profile

• Append the following lines:
  

  export JAVA_HOME=/opt/jdk-23.0.2
  export PATH=$JAVA_HOME/bin:$PATH

• Reload the configuration file:

  $ source ~/.profile

Verify the installation and environment variables:

$ java -version

openjdk version "23.0.2" 2025-01-21
OpenJDK Runtime Environment (build 23.0.2+7-58)
OpenJDK 64-Bit Server VM (build 23.0.2+7-58, mixed mode, sharing)

Locate the java executable:

$ which java
/opt/jdk-23.0.2/bin/java

The update-alternatives system allows you to manage multiple Java installations and switch between them easily.

1. Check defaults
   Check if alternatives are already configured:
   

   $ ls -al /usr/bin/java
   lrwxrwxrwx 1 root root /usr/bin/java -> /etc/alternatives/java

   $ ls -al /etc/alternatives/java
   lrwxrwxrwx 1 root root /etc/alternatives/java -> /usr/lib/jvm/java-17-openjdk-amd64/bin/java

   $ update-alternatives --list java

2. Add a new java alternative to the system
   Register your Java installation with update-alternatives (adjust paths as needed):

   $ sudo update-alternatives --install "/usr/bin/java" "java" "/opt/jdk-23.0.2/bin/java" 1
   $ sudo update-alternatives --install "/usr/bin/javac" "javac" "/opt/jdk-23.0.2/bin/javac" 1

   Display current alternatives:
   

   $ update-alternatives --display java
   java - auto mode
     link currently points to /usr/lib/jvm/java-17-openjdk-amd64/bin/java
   
   /opt/jdk-23.0.2/bin/java - priority 1
   /usr/lib/jvm/java-17-openjdk-amd64/bin/java - priority 1711
   
   Current 'best' version is '/usr/lib/jvm/java-17-openjdk-amd64/bin/java'.

3. Configure java alternatives
   Select which Java version to use as default:
   

   $ sudo update-alternatives --config java
   There are 2 choices for the alternative java (providing /usr/bin/java).
   
     Selection    Path                                        Priority   Status
   ------------------------------------------------------------
   * 0            /usr/lib/jvm/java-17-openjdk-amd64/bin/java  1711      auto mode
     1            /opt/jdk-23.0.2/bin/java                     1         manual mode
     2            /usr/lib/jvm/java-17-openjdk-amd64/bin/java  1711      manual mode
   
   Press <enter> to keep the current choice[*], or type selection number: 1
   update-alternatives: using /opt/jdk-23.0.2/bin/java to provide /usr/bin/java (java) in manual mode

   Also configure javac if you installed the compiler:
   

   $ sudo update-alternatives --config javac

4. Set JAVA_HOME dynamically
   Set JAVA_HOME to automatically point to the currently selected Java version:
   

   export JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:/bin/java::")

   Or add this to your shell profile for persistence:
   

   $ echo 'export JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:/bin/java::")' >> ~/.profile