This recipe shows how to install Java (JRE/JDK) on Ubuntu 20.04 LTS. These instructions are performed on a fresh Ubuntu Desktop/Server installation.
First update and upgrade the installed software packages on the system.
$ sudo apt update && sudo apt upgrade -y
Check if Java is already installed:
# Java Runtime Environment (JRE)
$ java -version
# Java Development Kit (JDK)
$ javac -version
If Java cannot be found on the system, then install the desired version(s):
# Java 8 JRE/JDK
$ sudo apt install openjdk-8-jre openjdk-8-jdk
# Java 11 JRE/JDK
$ sudo apt install openjdk-11-jre openjdk-11-jdk
If there are multiple versions of Java installed, you can configure which version to use as the default.
Type the following to show the list of currently installed java versions.
$ sudo update-alternatives --config java
You will see output such as:
$ 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-11-openjdk-amd64/bin/java 1111 auto mode
1 /usr/lib/jvm/java-11-openjdk-amd64/bin/java 1111 manual mode
2 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1081 manual mode
Press <enter> to keep the current choice[*], or type selection number:
Input the number associated with the version to use as the default and press ENTER.
Repeat the same steps for javac.
$ sudo update-alternatives --config javac
Add system-wide environment variables for JRE_HOME and JAVA_HOME in /etc/environment.
$ sudo nano /etc/environment
At the end of the file, add the following lines:
JRE_HOME="/usr/lib/jvm/java-8-openjdk-amd64/jre"
JAVA_HOME="/usr/lib/jvm/java-8-openjdk-amd64"
To apply the changes to your current session:
$ source /etc/environment
To verify that the environment variables are set properly, execute the following commands and confirm that the output matches the correct paths.
$ echo $JRE_HOME
$ echo $JAVA_HOME