How to Install Java on Ubuntu 20.04 LTS Linux

How to install Java on Ubuntu 20.04 LTS

Ubuntu Linux ships with OpenJDK version 8 and 14. Let us find out about versions using the apt-cache command and sort command:
$ apt-cache --names-only search 'openjdk-[0-9]*-(jre|jdk)' | sort -t '-' -k 2 -n
Different versions of JDK and JRE available for installation:

openjdk-8-jdk - OpenJDK Development Kit (JDK)
openjdk-8-jdk-headless - OpenJDK Development Kit (JDK) (headless)
openjdk-8-jre - OpenJDK Java runtime, using Hotspot JIT
openjdk-8-jre-headless - OpenJDK Java runtime, using Hotspot JIT (headless)
openjdk-8-jre-zero - Alternative JVM for OpenJDK, using Zero/Shark
openjdk-11-jdk - OpenJDK Development Kit (JDK)
openjdk-11-jdk-headless - OpenJDK Development Kit (JDK) (headless)
openjdk-11-jre - OpenJDK Java runtime, using Hotspot JIT
openjdk-11-jre-dcevm - Alternative VM for OpenJDK 11 with enhanced class redefinition
openjdk-11-jre-headless - OpenJDK Java runtime, using Hotspot JIT (headless)
openjdk-11-jre-zero - Alternative JVM for OpenJDK, using Zero
openjdk-13-jdk - OpenJDK Development Kit (JDK)
openjdk-13-jdk-headless - OpenJDK Development Kit (JDK) (headless)
openjdk-13-jre - OpenJDK Java runtime, using Hotspot JIT
openjdk-13-jre-headless - OpenJDK Java runtime, using Hotspot JIT (headless)
openjdk-13-jre-zero - Alternative JVM for OpenJDK, using Zero
openjdk-14-jdk - OpenJDK Development Kit (JDK)
openjdk-14-jdk-headless - OpenJDK Development Kit (JDK) (headless)
openjdk-14-jre - OpenJDK Java runtime, using Hotspot JIT
openjdk-14-jre-headless - OpenJDK Java runtime, using Hotspot JIT (headless)
openjdk-14-jre-zero - Alternative JVM for OpenJDK, using Zero

The headless version is for server users where you don’t need desktop GUI components of JAVA.

Step 1 – Installing OpenJDK version 14 on Ubuntu 20.04 LTS

Update the repo and then install the OpenJDK version 14 using the apt command:
$ sudo apt update
$ sudo apt upgrade
$ sudo apt install openjdk-14-jdk
## for servers try headless version ##
$ sudo apt install openjdk-14-jdk-headless

Installing OpenJDK version 14 on Ubuntu server

Step 2 – Verification

Let us print the Java version:
$ java --version

openjdk version "14.0.1" 2020-04-14
OpenJDK Runtime Environment (build 14.0.1+7-Ubuntu-1ubuntu1)
OpenJDK 64-Bit Server VM (build 14.0.1+7-Ubuntu-1ubuntu1, mixed mode, sharing)

Step 3 – Install multiple versions of Java/OpenJDK

We can install multiple versions on Ubuntu. It allows us to run different apps as per the Java version. For example, here I am going to install OpenJDK 11:
$ sudo apt install openjdk-11-jdk

Setting up the default Java version

We can use symbolic links to setup the default Java version. For example, change the default Java version, run the update-alternatives command:
$ sudo update-alternatives --config java
Make sure you type the number of the version you want using as the default Java and press the Enter key:

There are 2 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                         Priority   Status
------------------------------------------------------------
* 0            /usr/lib/jvm/java-14-openjdk-amd64/bin/java   1411      auto mode
  1            /usr/lib/jvm/java-11-openjdk-amd64/bin/java   1111      manual mode
  2            /usr/lib/jvm/java-14-openjdk-amd64/bin/java   1411      manual mode

Press  to keep the current choice[*], or type selection number: 1
update-alternatives: using /usr/lib/jvm/java-11-openjdk-amd64/bin/java to provide /usr/bin/java (java) in manual mode

I changed version to JDK 11. Let us print default version:
$ java --version

openjdk 11.0.8 2020-07-14
OpenJDK Runtime Environment (build 11.0.8+10-post-Ubuntu-0ubuntu120.04)
OpenJDK 64-Bit Server VM (build 11.0.8+10-post-Ubuntu-0ubuntu120.04, mixed mode, sharing)

Step 4 – Set up JAVA_HOME environment variable

The syntax is as follows using the export command for bash:
export JAVA_HOME=/path/to/openjdk
# For OpenJDK version 14 #
export JAVA_HOME=/usr/lib/jvm/java-14-openjdk-amd64
# For OpenJDK version 11 #
export JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64

Display the settings using the echo command/printf command:

echo $JAVA_HOME
printf "Java HOME PATH : %s\n" $JAVA_HOME

Finally, update the environment variables config file and set JAVA_HOME as follows:
$ sudo vim /etc/environment
## OR ##
$ sudo nano /etc/environment
Append the settings:
JAVA_HOME="/usr/lib/jvm/java-11-openjdk-amd64"
Save and close the file.

How to set JAVA_HOME for individual users

The JAVA_HOME set in /etc/environment file is for all Linux users. However, individual users and apps can override JAVA_HOME and PATH settings using the ~/.bash_profile or ~/.bashrc. For instance, Linux user can append PATH settings to end of file as follows:

echo "export JAVA_HOME='/usr/lib/jvm/java-11-openjdk-amd64'" >> ~/.bashrc
echo "export PATH='$PATH:/usr/lib/jvm/java-11-openjdk-amd64/bin'" >> ~/.bashrc

Step 5 – Testing your Java version by writing “Hello World” program

Create a new file called HelloWorld.java using a text editor such as vim/nano:
$ vim HelloWorld.java
Append the following code:

// Old good Hello World in Java:
// https://docs.oracle.com/javase/tutorial/getStarted/application/index.html
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
 
public class HelloWorld {
  public static void main(final String[] args) {
    final DateTimeFormatter dtf = DateTimeFormatter.ofPattern("h:mm:ss a 'on' MMMM d, yyyy'.'");
    final LocalDateTime now = LocalDateTime.now();
    System.out.println("Hello, World! The current time is " + dtf.format(now));
  }
}

Run it:
java HelloWorld.java

Hello, World! The current time is 8:47:20 AM on September 12, 2020.

Conclusion

This tutorial explained how to install different versions of Java and manage them using the CLI. Once Java is installed, we can write an application. Moreover, your Ubuntu 20.04 LTS is now ready to install other popular opensource apps such as Tomcat.