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