Environment Variable :

change(import) /etc/bashrc

    export JAVA_HOME=/software/jdk1.8.0

    export PATH=$JAVA_HOME/bin:$PATH

    export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar

save and exit.

Change default JDK:

    update-alternatives --install /usr/bin/java java /software/jdk1.8.0/bin/java 300

    update-alternatives --install /usr/bin/javac javac /software/jdk1.8.0/bin/javac 300

    update-alternatiives --config java

    [and then you can choose jdk version.]

Test :

    terminal: java -version