How to set the default Java version on Linux

1. Open a new Terminal Window
2. Execute the following command:

   sudo update-alternatives --config java

3. Output similar to the below will show:

   There are 4 choices for the alternative java (providing /usr/bin/java).
   
     Selection    Path                                            Priority   Status
   ------------------------------------------------------------
     0            /usr/lib/jvm/java-8-oracle/jre/bin/java          1092      auto mode
   * 1            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1071      manual mode
     2            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1081      manual mode
     3            /usr/lib/jvm/java-8-oracle/jre/bin/java          1092      manual mode
     4            /usr/lib/jvm/java-9-openjdk-amd64/bin/java       1091      manual mode
   
   Press <enter> to keep the current choice[*], or type selection number:

4. Enter the number next to your preferred version and hit the Enter key
5. Now the default Java version will be changed.