Plasma simulation is an important example of a high-performance computing application where computer science issues are of great relevance. In a plasma, each particle, electron or ion, interacts with the external fields and with other particles in ways that can be readily and effectively emulated using object-oriented programming. However, the great cost of plasma simulations has traditionally discouraged object-oriented implementations due to their perceived inferior performance compared with classic procedural FORTRAN or C. In the present paper, we revisit this issue. We have developed a Java particle-in-cell code for plasma simulation, called Parsek. The paper considers different choices for the object orientation and tests their performance. We find that coarse-grained object orientation is faster and practically immune from any degradation compared with a standard procedural implementation (with static classes). The loss in performance for a fine-grained object orientation is a factor of about 50%, which can be almost completely eliminated using advanced Java compilation techniques. The Java code Parsek also provides an interesting realistic application of high-performance computing to compare the performance of Java with FORTRAN. We have conducted a series of tests considering various Java implementations and various FORTRAN implementations. We have also considered different computer architectures and different Java Virtual Machines and FORTRAN compilers. The conclusion is that with Parsek, object-oriented Java can reach CPU speed performances more or less comparable with procedural FORTRAN. This conclusion is remarkable and it is in agreement with the most recent benchmarks, but is at variance with widely held misconceptions about the alleged slowness of Java.