Downgrading Java 11 to java 8?

Question

How can i downgrade the java version 11 to java 8. As i need jenkins, current jenkins versoin doesn't support java 11. I need to downgrade.

Answer 1

1. You have to install the openjdk-8-jre:

    sudo apt-get install openjdk-8-jre
   

2. Next switch to the jre-8 version:

    $ 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-9-openjdk-amd64/bin/java       1500      auto mode
   1            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1500      manual mode
   2            /usr/lib/jvm/java-9-openjdk-amd64/bin/java       1500      manual mode
   
   

3. Add JAVA_HOME variable:

    export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64
   

4. check java version:

    $ java -version
    openjdk version "1.8.0_151"
    OpenJDK Runtime Environment (build 1.8.0_151-8u151-b12-0ubuntu0.17.10.2-b12)
    OpenJDK 64-Bit Server VM (build 25.151-b12, mixed mode)
   

Same procedure for Oracle java.