I wonder how you got Eclipse 3 to recognise any of the new language constructs.
Developing programs with J2SE 1.5
The Java tools do not yet fully support J2SE 1.5. You can run or debug programs against a 1.5 JRE, and safely compile 1.4 programs against 1.5 libraries (the Eclipse compiler tolerates them with the exception of covariance scenarios which are forbidden byJava Language Specification (JLS) 2nd edition). However, the Eclipse Java compiler and IDE are unable to handle source files containing uses of any of the new Java language features being added in 1.5 (generics, enhanced for loops, static imports, metadata annotations, varargs), which will be codified in the forthcoming JLS 3rd edition. An early preview of the full Eclipse support for J2SE 1.5 developed in parallel with 3.0, and is available from the Cheetah page. (bug 36938)
These release notes have yet to be updated for the 3.1 development stream.
What follows are the 3.0.0 release notes.]
If you had installed additional features and plug-ins into your old Eclipse, you should re-install them in the new Eclipse