Looks like WordPress is/was completely ported to a Java based system via nTilePtoJ optimization algorithms, including type inference, transformation of dynamic constructs, object extraction and variable scope optimization..

Even more improving is on it’s way:

• improve the code quality and enforce sanity checks using static analysis tools (like PMD, FindBugs)
• in particular, find a better alternative to the current inherited framework for defining and applying filters (dynamic function invocations) – OSGi services or Equinox extension points come to mind
• start migrating relevant existing WordPress extensions
• …

Wonder how they apply the migrating of extensions, as all are working with php WP core codes,
however sounds like an interesting project.

Get it at SourceForge and try it out.