default-java.md

Set Default Java Version

Install Java.

sudo apt install openjdk-8-jre
sudo apt install openjdk-11-jre

Set the default version.

sudo update-alternatives --set java /usr/lib/jvm/java-11-openjdk-amd64/bin/java

List the alternatives.

update-alternatives --list java
/usr/lib/jvm/java-11-openjdk-amd64/bin/java
/usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java

Confirm.

which java
/usr/bin/java
java -version
openjdk version "11.0.11" 2021-04-20
OpenJDK Runtime Environment (build 11.0.11+9-Ubuntu-0ubuntu2.20.04)
OpenJDK 64-Bit Server VM (build 11.0.11+9-Ubuntu-0ubuntu2.20.04, mixed mode, sharing)

To configure the Java runtime interactively, use the --config switch.

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:

References

1. How to Install OpenJDK 11 in Ubuntu 18.04
2. How to use the command update-alternatives --config java
3. OpenJDK 8 Download and Installation on Ubuntu