How to use the command update-alternatives --config java

Question

I am installing Apache Solr on Linux Debian (Squeeze). I have been instructed to install sun-java jdk 1st. Then am told that I should use the command sudo update-alter

Answer 1

I'm using Ubuntu 18.04 LTS. Most of the time, when I change my java version, I also want to use the same javac version.
I use update-alternatives this way, using a java_home alternative instead :

Installation

Install every java version in /opt/java/, for example

~$ ll /opt/java/
total 24
drwxr-xr-x 6 root root 4096 jan. 22 21:14 ./
drwxr-xr-x 9 root root 4096 feb.  7 13:40 ../
drwxr-xr-x  8 stephanecodes stephanecodes 4096 jan.   8  2019 jdk-11.0.2/
drwxr-xr-x  7 stephanecodes stephanecodes 4096 dec.  15  2018 jdk1.8.0_201/

Configure alternatives

~$ sudo update-alternatives --install /opt/java/current java_home /opt/java/jdk-11.0.2/ 100
~$ sudo update-alternatives --install /opt/java/current java_home /opt/java/jdk1.8.0_201 200

Declare JAVA_HOME (In this case, I use a global initialization script for this)

~$ sudo sh -c 'echo export JAVA_HOME=\"/opt/java/current\" >> environment.sh'

Log Out or restart Ubuntu (this will reload /etc/profile.d/environment.sh)

Usage

Change java version

Choose the version you want to use

~$ sudo update-alternatives --config java_home

There are 2 choices for the alternative java_home (providing /opt/java/current).

  Selection    Path                    Priority   Status
------------------------------------------------------------
  0            /opt/java/jdk-11.0.2     200       auto mode
  1            /opt/java/jdk-11.0.2     200       manual mode
* 2            /opt/java/jdk1.8.0_201   100       manual mode

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

Check version

~$ java -version
openjdk version "11.0.2" 2019-01-15
OpenJDK Runtime Environment 18.9 (build 11.0.2+9)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.2+9, mixed mode)

~$ javac -version
javac 11.0.2

Tip

Add the following line to ~/.bash_aliases file :

alias change-java-version="sudo update-alternatives --config java_home && java -version && javac -version"

Now use the change-java-version command to change java version