Thanks for your replies. So no interaction it will be.The package I am thinking about is supposed to install itself in the JRE directory (java). Some configuration have a JAVA_HOME variable set, which allows the PKGBUILD to decide for the user, but some do not have it.
I've Installed oracle JDK version 1.8 on a debian machine that already has openjdk 1.6.i've set the path variable in etc/login.defs and java_home variable In etc/environment.
When I echo $JAVA_HOME it points to the oracle version correctly and when I run javac It uses the oracle 1.8 version.