Check which java versions are installed on your system (JRE & JDK)
$ /usr/libexec/java_home -V
Run the line below in your terminal. Just replace version's number with the one you want (in this case 1.8)
$ export JAVA_HOME=`/usr/libexec/java_home -v 1.8`
If you have multiple subversions of Java, it will choose the highest available if you don't specify one.
then verify your version running with
$ java -version