Java 5 is the same on all platforms, so there's no special docs for the Mac. In fact, they should be installed on your machine already; point your browser at
file:///System/Library/Frameworks/JavaVM.framework/Versions/1.5.0/Home/doc/api/index.html
and
file:///System/Library/Frameworks/JavaVM.framework/Versions/1.6.0/Home/docs/api/index.html
for Java 5 and 6 docs, respectively.