I am trying to update my eclipse environment to java 8. I installed the jdk and jre version 8. I also did this:
https://wiki.eclipse.org/JDT/Eclipse_Java_8_Support_
I would like to precise something. If you installed java8 with apt-get like me, the jdk is add to /usr/lib/jvm.
In OS X, go to Preference and choose Java | Installed JREs. Then click search it would show JAVA SE 8 if you have already installed JAVA SDK 8.

Go to Window | Preferences. Then under Java | Installed JREs, click "Add", click "Standard VM", then "Next", then "Directory", and find the location where you installed JDK 1.8.
Lastly, make sure the checkbox next to it, on the list of installed JREs, is switched on.