This paper describes experiences in using an O.O. language (Java) in designing, prototyping and evaluating a CPU manager. QoS Animator facilitates the execution of object oriented Java applications with time requirements and provides protection mechanisms to preserve system' s integrity against untrusted code. It is adapted to the system performance and provides a rate-monotonic based scheduling algorithm, WCET calculation at run-time and protection from high-CPU-consuming and "bad" code. The introduction of the Low Frequency Filter enhances the timeliness offered to applications in general-purposes Operating Systems (OS). The evaluation was done with a Windows NT specific prototype and proved successful.