Other ongoing projects that extend the Java language to directly support scientific parallel computation include Titanium  from UC Berkeley, Timber/Spar  from Delft University of Technology, and Jade  from University of Illinois at Urbana-Champaign.
Titanium adds a comprehensive set of parallel extensions to the Java language. For example it includes support for a shared address space, and does compile-time analysis of patterns of synchronization. This contrasts with our HPJava, which only adds new data types that can be implemented ``locally'', and leaves all interprocess communication issues to the programmer and libraries.
The Timber project extends Java with the Spar primitives for scientific programming, which include multidimensional arrays and tuples. It also adds task parallel constructs like a foreach construct.
Jade focuses on message-driven parallelism extracted from interactions between a special kind of distributed object called a Chare. It introduces a kind of parallel array called a ChareArray. Jade also supports code migration.
HPJava differs from these projects in emphasizing a lower-level (MPI-like) approach to parallelism and communication, and by importing HPF-like distribution formats for arrays. Another significant difference between HPJava and the other systems mentioned above is that HPJava translates to Java byte codes, relying on clusters of conventional JVMs for execution. The systems mentioned above typically translate to C or C++. While HPJava may pay some price in performance for this approach, it tends to be more fully compliant with the standard Java platform (e.g. it allows local use of Java threads, and APIs that require Java threads).