MPJ Express is a messaging system that allows application developers to parallelize their compute-intensive sequential Java codes on High Performance Computing clusters and multicore processors. In this paper, we extend MPJ Express software to provide two new communication devices. The first device-called hybrid-enables MPJ Express to exploit hybrid parallelism on cluster of multicore processors by sitting on top of existing shared memory and network communication devices. The second device-called native-uses JNI wrappers in interfacing MPJ Express to native MPI implementations like MPICH and Open MPI. We evaluate performance of these devices on a range of interconnects including 1G/10G Ethernet, 10G Myrinet and 40G InfiniBand. In addition, we analyze and evaluate the cost of MPJ Express buffering layer and compare it with the performance numbers of other Java MPI libraries. Our performance evaluation reveals that the native device allows MPJ Express to achieve comparable performance to native MPI libraries-for latency and bandwidth of point-to-point and collective communications-which is a significant gain in performance compared to existing communication devices. The hybrid communication device-without any modifications at application level-also helps parallel applications achieve better speedups and scalability by exploiting multicore architecture. Our performance evaluation quantifies the cost incurred by buffering and its impact on overall performance of software. We witnessed comparative performance as both new devices improve application performance and achieve upto 90 % of the theoretical bandwidth available without application rewriting effort-including NAS Parallel Benchmarks, point-to-point and collective communication.