How to install the JDK on Ubuntu Linux

1. Open Terminal from Application Dash or press Ctrl+Alt+T
2. Update repository:

   sudo add-apt-repository ppa:openjdk-r/ppa  # only Ubuntu 17.4 and earlier
   sudo apt update

3. Optional: To search available distributions of openjdk, use the following command:

   apt search openjdk

4. Install the appropriate version with the following command:

   sudo apt install openjdk-8-jdk
   sudo apt install openjdk-8-source #this is optional, the jdk source code

5. For JAVA_HOME (Environment Variable) type command as shown below, in "Terminal" using your installation path...

   export JAVA_HOME=/usr/lib/jvm/java-8-openjdk

   (Note: /usr/lib/jvm/java-8-openjdk is symbolically used here just for demostration. You should use your path as per your installation.)
6. For PATH (Environment Variable) type command as shown below, in Terminal:
   export PATH=$PATH:$JAVA_HOME/bin
7. To check your installation:
   java -version