The development of Eclipse support for Java 8 is ongoing in a branch (http://wiki.eclipse.org/JDT_Core/Java8).
To try out the current Eclipse support for Java 8, I d
Eclipse version >=Luna (that's one after Kepler) runs smoothly with java 8.
If you have Kepler you can get it using a patch that has installation instructions on this page:
https://wiki.eclipse.org/JDT/Eclipse_Java_8_Support_For_Kepler
Starting with I20140318-0830 all Luna (4.4) builds on our downloads page contain the Eclipse support for Java™ 8. For Kepler SR2 (4.3.2) a feature patch needs to be installed. This page describes how to do this.
I just went to the Eclipse Marketplace from inside of Eclipse (Help/Eclipse Marketplace...) and installed the "Java 8 support for Eclipse Kepler SR2", and the new "JavaSE-1.8" execution environment showed up automatically. I had previously installed Java 8 and added it as a 'Installed JREs' entry. No need to mess with property files.
Think you just have to change the 'settings' directly in the 'preference file' : org.eclipse.jdt.core.prefs
.
e.g. org.eclipse.jdt.core.compiler.compliance=1.8