How to switch java version on ubuntu 20.04

• View all java versions

lwk@qwfys:~$ update-java-alternatives --list
java-1.11.0-openjdk-amd64      1111       /usr/lib/jvm/java-1.11.0-openjdk-amd64
java-1.8.0-openjdk-amd64       1081       /usr/lib/jvm/java-1.8.0-openjdk-amd64
lwk@qwfys:~$

• switch java version

lwk@qwfys:~$ 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: 1
update-alternatives: using /usr/lib/jvm/java-11-openjdk-amd64/bin/java to provide /usr/bin/java (java) in manual mode
lwk@qwfys:~$

• step write JAVA_HOME to file

lwk@qwfys:~$ echo $"export JAVA_HOME=$(readlink -f /usr/bin/java | sed 's:jre/bin/java::')" |sudo tee /etc/profile.d/java.sh
export JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64/bin/java
lwk@qwfys:~$

• step Activate variable value

. /etc/profile.d/java.sh

• step View the changed value

lwk@qwfys:~$  echo $JAVA_HOME
/usr/lib/jvm/java-11-openjdk-amd64/bin/java 
lwk@qwfys:~$