When the JVM exits, the memory used for the java heap is not released back to the O/S. For applications launched from the command line with 'java' this is not a problem because the O/S reclaims all resources used by the process after it terminates. However, applications that use the JNI invocation api to start the JVM and that continue to run after the JVM exits will see that the java heap memory (which can be very large) has been leaked.