In this paper, the authors introduce the concept of a Java processor for embedded real-time systems, in particular the design of a small processor for resource-constrained devices with time-predictable execution of Java programs. This Java processor is called JOP - which stands for Java Optimized Processor -, based on the assumption that a full native implementation of all Java bytecode instructions is not a useful approach. Worst-Case Execution Time (WCET) estimates of tasks are essential for designing and verifying real-time systems. Static WCET analysis is necessary for hard real-time systems. In order to obtain a low WCET value, a good processor model is necessary. Traditionally, only simple processors can be analyzed using practical WCET boundaries.