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In this guide, I’ll show you how you can set the default Java version on Ubuntu / Debian. It is common to run more than one version of Java in your Ubuntu or Debian system – For development reasons or varying applications requirements.

Earlier on we had done an article on installing Java 11 on Ubuntu / Debian: How to Install Java 11 on Ubuntu 18.04 /16.04 / Debian 9

For Java 8: How to Install Java 8 on Ubuntu

Suppose you install Java 11 and you had another version of Java installed earlier, you can select default Java version to use using the update-alternatives --config java command.

Checking Java versions installed on Ubuntu / Debian

To get a list of installed Java versions, run the command:

$ update-java-alternatives --list
java-1.11.0-openjdk-amd64 1101 /usr/lib/jvm/java-1.11.0-openjdk-amd64
java-8-oracle 1081 /usr/lib/jvm/java-8-oracle

Once you have a list of Java version, set a default one by running the 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   1101      auto mode
* 1            /usr/lib/jvm/java-11-openjdk-amd64/bin/java   1101      manual mode
  2            /usr/lib/jvm/java-8-oracle/jre/bin/java       1081      manual mode

Press <enter> to keep the current choice[*], or type selection number: 2

Check Java version

$ java -version
java version "1.8.0_191"
Java(TM) SE Runtime Environment (build 1.8.0_191-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.191-b12, mixed mode)

The same can be done for javac.

~$ sudo  update-alternatives --config javac

There is 1 choice for the alternative javac (providing /usr/bin/javac).

  Selection    Path                                  Priority   Status
------------------------------------------------------------
  0            /usr/lib/jvm/java-8-oracle/bin/javac   1081      auto mode
* 1            /usr/lib/jvm/java-8-oracle/bin/javac   1081      manual mode

Press <enter> to keep the current choice[*], or type selection number: 

If JAVA_HOME is not set correctly, run the command below to set from current default Java configured.

export JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:bin/java::")

For JRE, use:

export JAVA_HOME=$(readlink -f /usr/bin/java | sed "s:jre/bin/java::")

Persistence can be achieved by placing the export command in your .bashrc or /etc/profilefile.

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