Designing a simple but powerful low-level communication library for Java HPC environments is an important task. We introduce new low-level communication library for Java HPC, called mpjdev. The mpjdev API is designed with the goal that it can be implemented portably on network platforms and efficiently on parallel hardware. Unlike MPI which is intended for the application developer, mpjdev is meant for library developers. Application level communication may be implemented on top of mpjdev. The mpjdev API itself might be implemented on top of Java sockets in a portable network implementation, or-on HPC platforms-through a JNI (Java Native Interface) to a subset of MPI.