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.]

Second Method: replace file

　　ln -s -f /usr/local/jdk1.6.0_24/jre/bin/java

　　ln -s -f /usr/local/jdk1.6.0_24/bin/javac

Test :

terminal: java -version