Java is a software platform that allows the compilation and execution of software written in Java language. Java features a cross-platform to compile and execute applications no matter what the hardware in use is.
In this tutorial you will find all the necessary steps to install and configure Java Runtime Environment and Java Development Kit to compile or run Java software on Linux Ubuntu 20.04.
First, connect to your server via an SSH connection. If you haven’t done so yet, following our guide is recommended to connect securely with SSH. In case of a local server, go to the next step and open the terminal of your server.
Installing Java - JRE
Verify that Java is not already installed with the following command:
If the following message appears on the screen:
Java is not installed on the system. So, proceed with the installation of the Java Runtime Environment which runs most Java softwares.
Update the distribution repositories, to be sure you download the latest version of the packages:
Then, start the installation of the Java Runtime Environment:
$ sudo apt install default-jre
At this point, check the correct installation:
If the installation was successful, the command will show the version number of the JRE.
Installing OpenJDK
To use the Java Development Kit to compile or run Java software, proceed with its installation in this way:
$ sudo apt install default-jdk
Check the installation by showing the version number of javac, the Java compiler:
If the installation was successful, the version number of javac will be shown:
Managing multiple versions of Java
You can set the default Java version using the update-alternatives command:
$ sudo update-alternatives --config java
This selection screen will be shown:
There are 3 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-11-openjdk-amd64/bin/java 1101 auto mode
1 /usr/lib/jvm/java-11-openjdk-amd64/bin/java 1101 manual mode
2 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1081 manual mode
3 /usr/lib/jvm/java-8-oracle/jre/bin/java 1081 manual mode
Type the number associated with the Java version of your preference you to set it as ‘default’ or press ENTER to keep the current version as default.
Setting the JAVA_HOME environment variable
Different software use the JAVA_HOME variable to locate the version of java to be used.
To set the version to use, first, check the current Java installations on the system using the update-alternatives command:
$ sudo update-alternatives --config java
The following screen, showing the path of each Java installation, will be displayed:
There are 3 choices for the alternative java (providing /usr/bin/java).
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/jvm/java-11-openjdk-amd64/bin/java 1101 auto mode
1 /usr/lib/jvm/java-11-openjdk-amd64/bin/java 1101 manual mode
2 /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java 1081 manual mode
3 /usr/lib/jvm/java-8-oracle/jre/bin/java 1081 manual mode
For example, o use version 11, copy the following path:
/usr/lib/jvm/java-11-openjdk-amd64/bin/
Now edit the /etc/ environment file:
$ sudo nano /etc/environment
and, at the end of the file, add the following line:
JAVA_HOME="/usr/lib/jvm/java-11-openjdk-amd64/bin/"
Save and close the file.
At this point, the path relative to the JAVA_HOME variable for all the users of the system, will have been modified
Reload the file with the source command to apply the changes:
$ source /etc/environment
and check whether the variable has been correctly set by printing it on the screen.
/usr/lib/jvm/java-11-openjdk-amd64/bin/