X Windows Is There
At least if it was installed before. The good news is that it's using xorg-server 1.10.2, which enables a few extensions used by modern X software. So, for example, you're ssh'ing over to Linux box and use Emacs, you won't get the warnings that you used to.
It's not entirely Lion-ized, though. For example, you can only resize a window from the lower right using the old resize control.
Java Is There, and the Developer Kit Download Might Not Be Needed
After the recent Java Drama in the Leopard versions of Mac OS X, Apple started delivering the sources and native headers for Java in a separate download on {{developer.apple.com}}, which was annoying if you were compiled JNI modules.
In Mac OS X Lion, Java is not included, but, as you as you start a Java program (any Eclipse or RCP-based application, for example), you'll be offered to download it. As before, “Java” on Mac OS X really means the JDK, not just the JRE. But it also looks like the JNI headers are included in this civilian download as well, which is a welcome restoration of affairs.
The current version is the same as Snow Leopard's: 6u26. This has an escape-analysis-related JIT bug that can affect long-running applications; version 6u27 is supposed to fix this.
GCC 4.2 from Xcode 4.1 Uses The LLVM Front End
Notice:
$ gcc --version i686-apple-darwin11-llvm-gcc-4.2 (GCC) 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2335.15.00)
This shouldn't break anything, unless, I suspect, you have truly pathological C or C++ code. Since the GCC 4.2 backend is still used, you can safely link with GCC-compiled libraries from the GCC front-end version of GCC 4.2
