Ubuntu
Execute the following command to install the default Java Runtime Environment (JRE), which will install the JRE from OpenJDK 11:
$ apt install default-jre
The JRE will allow you to run almost all Java software.
Verify the installation with:
$ java -version
You’ll see the following output:
Outputopenjdk version "11.0.7" 2020-04-14
OpenJDK Runtime Environment (build 11.0.7+10-post-Ubuntu-2ubuntu218.04)
OpenJDK 64-Bit Server VM (build 11.0.7+10-post-Ubuntu-2ubuntu218.04, mixed mode, sharing)
You may need the Java Development Kit (JDK) in addition to the JRE in order to compile and run some specific Java-based software. 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:
$ javac -version
You’ll see the following output:
Outputjavac 11.0.7
Setting the JAVA_HOME Environment Variable
Many programs written using Java use the JAVA_HOME environment variable to determine the Java installation location.
To set this environment variable, first determine where Java is installed. Use the update-alternatives command:
sudo update-alternatives --config java
This command shows each installation of Java along with its installation path:
OutputThere 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-11-oracle/bin/java 1091 manual mode
Press <enter> to keep the current choice[*], or type selection number:
In this case the installation paths are as follows:
- OpenJDK 11 is located at
/usr/lib/jvm/java-11-openjdk-amd64/bin/java. - Oracle Java is located at
/usr/lib/jvm/java-11-oracle/jre/bin/java.
Copy the path from your preferred installation. Then open /etc/environment using nano or your favorite text editor:
sudo nano /etc/environment
At the end of this file, add the following line, making sure to replace the highlighted path with your own copied path, but do not include the /bin portion of the path:
/etc/environment
JAVA_HOME="/usr/lib/jvm/java-11-openjdk-amd64/bin/java"
Modifying this file will set the JAVA_HOME path for all users on your system.
Save the file and exit the editor.
Now reload this file to apply the changes to your current session:
source /etc/environment
Verify that the environment variable is set:
echo $JAVA_HOME
You’ll see the path you just set:
Output/usr/lib/jvm/java-11-openjdk-amd64
Other users will need to execute the command source /etc/environment or log out and log back in to apply this setting.