Java using up far more memory than allocated with -Xmx

Question

I have a project I\'m writing (in Java) for a class where the prof says we\'re not allowed to use more than 200m I limit the stack memory to 50m (just to be absolutely sure)

Answer 1

Top command reflects the total amount of memory used by the Java application. This includes among other things:

• A basic memory overhead of the JVM itself
• the heap space (bounded with -Xmx)
• The permanent generation space (-XX:MaxPermSize - not standard in all JVMs)
• threads stack space (-Xss per stack) which may grow significantly depending on the number of threads
• Space used by native allocations (using ByteBufer class, or JNI)