No need to unistall java 8
Ok the easiest way to do this is to run this in you terminal
export JAVA_HOME=`/usr/libexec/java_home -v 1.8`
cd /Users/yourname/Desktop/Technic
java -jar TechnicLauncher.jar
make sure you replace your name with what ever the location is
also make sure technic is on your desktop or else change the location
the point is to cd the location of the technic file i put it in a folder called technic for my use of ease
But Running this from terminal every time you want to use technic suck so what you need to do is to go into automator and search run click run shell script then insert the code you use
I hope this helped you