Since the OBS paradigm has become a potential candidate to cope with the needs of the future all optical networks, it has really caught the attention from both academia and industry worldwide. In this direction, OBS networks have been investigated under many different scenarios comprising numerous architectures and strategies. This heterogeneous context encourages the development of flexible simulation tools. These tools should permit both an easy integration of any possible new network protocol design and a rapid adaptation to different performance target goals. In this paper, we present two OBS network simulators, namely, a C-based simulator (ADOBS) and our novel Java-based simulator (JAVOBS). We compare their performances and we provide some exemplary results that point out remarkable flexibility that can be achieved with the JAVOBS simulator.