Config JDK environtment variables
Open /root/.bash_profile through your text editor.
vi /root/.bash_profile
And paste the given below two lines
export JAVA_HOME=/usr/java/jdk1.8.0_121
export PATH=/usr/java/jdk1.8.0_121/bin:$PATH
Now enable the Java variable without system restart (On system restart it bydefault set the java variable)
source /root/.bash_profile
Now check the Java version,JAVA_HOME and PATH variables.It should show you correct information as you have set.
java --version
echo $JAVA_HOME
echo $PATH
Other way:
cd /etc/alternatives/
rm java
y
ln -s /usr/java/jdk1.8.0_121/bin/java java