Ever since its introduction from Sun Microsystems four years ago (1996), Java has been widely accepted in the computing and Internet industry. However, the runtime performance is still not good enough for Java to become a general-purpose programming language. The article shows how to implement a Java microprocessor core in silicon to speed up the execution of Java. For a reconfigurable and flexible design, the field programmable gate array is chosen as a target technology for the Java microprocessor. By applying a top-down hardware design methodology to the FPGA design process, it becomes easier and more flexible to implement Java in a FPGA. The DFT technique is added for better testability.