Assuming you use bash shell and installed Java with the Oracle installer, you could add the following to your .bash_profile
export JAVA_HOME=$(/usr/libexec/java_home)
export PATH=$JAVA_HOME/jre/bin:$PATH
This would pick the correct JAVA_HOME as defined by the Oracle installer and will set it first in your $PATH making sure it is found.
Also, you don’t need to change it later when updating Java.
EDIT
As per the comments:
Making it persistent after a reboot
Just add those lines in the shell configuration file. (Assuming it’s bash)
Ex: .bashrc, .bash_profile or .profile (for ubuntu)
Using a custom Java installation
Set JAVA_HOME to the root folder of the custom Java installation path without the $().
Ex: JAVA_HOME=/opt/java/openjdk
