On Yosemite the upgrade de-installed it and installed Java 7.
(I am at the office so cannot give the link) (Google is your friend....) but found Java runtime 6. Downloaded it and IDE works fine.
Note that my edison is one of a new batch that came to sparkfun - The instruction for config did not match the image that was on the edison so.... Re-flashed the image and compatibility with setup instructions came back (Configure_edison --setup etc).
Moral of story - reflash latest Yocto before doing anything.
(The installed image had some 'weirdness' - the first character I typed seemed to get lost - bit of a pain when trying to type in root password)