Installation of Java in Ubuntu 18.04

In this guide:

default JRE/JDK installation;
installation of specific OpenJDK versions;
Oracle JDK installation;
switching between Java versions;
setting the JAVA_HOME environment variable.

Java is an object-oriented programming language that Sun Microsystems started developing in 1991. It was officially released on May 23, 1995. The language was originally called Oak (by its creator James Gosling) and was designed for home electronics. Later it was renamed Java and became popular for applets, desktop applications and server software.

A key feature of Java is its flexible security model: programs run under the control of the Java virtual machine, and any operation beyond the permissions of the program, such as unauthorized access to data or connections to other computers, is stopped immediately.

Default JRE/JDK Installation

The easiest way is to install the OpenJDK version from the Ubuntu repository. OpenJDK is the open-source implementation of the JRE and JDK. On Ubuntu 18.04 the default version is OpenJDK 11.

Update the package index:

sudo apt update

Check whether Java is already installed:

java -version

If Java is not installed, you will see:

Command 'java' not found, but can be installed with:

apt install default-jre
apt install openjdk-11-jre-headless
apt install openjdk-8-jre-headless

Install the Java Runtime Environment (JRE), which is enough to run most Java applications:

sudo apt install default-jre

Check the installation:

java -version

openjdk version "11.0.6" 2020-01-14
OpenJDK Runtime Environment (build 11.0.6+10-post-Ubuntu-1ubuntu118.04.1)
OpenJDK 64-Bit Server VM (build 11.0.6+10-post-Ubuntu-1ubuntu118.04.1, mixed mode, sharing)

To compile and run some Java programs, you also need the Java Development Kit (JDK). This command installs the JDK together with the JRE:

sudo apt install default-jdk

Check the version of the Java compiler:

javac -version

javac 11.0.6

Installing Specific OpenJDK Versions

OpenJDK 8

sudo apt install openjdk-8-jdk

To install only the JRE:

sudo apt install openjdk-8-jre

OpenJDK 11

sudo apt install openjdk-11-jdk

To install only the JRE:

sudo apt install openjdk-11-jre

Oracle JDK Installation

Old guides use the webupd8team/java PPA and the oracle-java8-installer package. This PPA was closed in 2019 and no longer works. Oracle now provides .deb packages, so download the package from oracle.com and install it with apt, for example:

wget https://download.oracle.com/java/21/latest/jdk-21_linux-x64_bin.deb
sudo apt install ./jdk-21_linux-x64_bin.deb

Switching Between Java Versions

One server can have several Java versions. To set the default one, use the update-alternatives command:

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:

Enter the number of the default Java version, or press Enter to keep the current setting. You can do the same for other Java commands, for example the javac compiler:

sudo update-alternatives --config javac

Setting the JAVA_HOME Environment Variable

First, find the installation directory with update-alternatives (see above). Copy the path of the version you need without /bin/java at the end. Then open /etc/environment in a text editor:

sudo nano /etc/environment

Add the following line at the end of the file. JAVA_HOME must point to the JDK root directory, not to its bin directory:

JAVA_HOME="/usr/lib/jvm/java-11-openjdk-amd64"

This sets JAVA_HOME for all users. Save the file and exit nano (Ctrl+O, Enter, Ctrl+X). Reload the file to apply the changes to the current session:

source /etc/environment

Check the variable:

echo $JAVA_HOME

/usr/lib/jvm/java-11-openjdk-amd64

Other users need to run source /etc/environment or log in again to apply the setting. For newer Ubuntu versions, see our guide on how to install Java on Ubuntu.

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