By default, Ubuntu 18.04 includes OpenJDK version 11,which is an open-source variant of the JRE and JDK.
To install this version, first update the package index with below command.
#sudo apt update
Then execute below commands based on which version you want to install.
#apt install default-jre : For Defauly version.
#apt install openjdk-11-jre-headless : For Java 11
#apt install openjdk-8-jre-headless : For Java 8
Verify the Java installation with below command.
#java -version
To install the JDK, execute the following command, which will also install the JRE.
#sudo apt install default-jdk
Verify that the JDK is installed by checking the version of javac, the Java compiler using below command.
#javac -version
To Install the Open JDK 8, use the below command.
#sudo apt install openjdk-8-jdk
