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_For_Kepler
then in project -> properties -> java build path -> JRE system libraries -> edit -> execution environment -> JavaSE-1.8(unbound) which is the only option that has java 8 in its name. but when I select it it says : No JREs in workspace compatible with specified execution environment: JavaSE-1.8
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.
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.
I would like to precise something. If you installed java8 with apt-get like me, the jdk is add to /usr/lib/jvm.
来源：https://stackoverflow.com/questions/22619262/upgrade-eclipse-to-java-8