JVM architecture

JVM architecture can be described in terms of the runtime data structure in the memory and in terms of the two subsystems that use the runtime data – the classloader and execution engine.

Runtime data areas

Each of the runtime data areas of JVM memory belong to one of two categories:

• Shared areas, which include the following:
  • Method area: Class metadata, static fields, methods bytecodes
  • Heap area: Objects (state)
• Not shared areas, dedicated to each application thread, which include the following:
  • Java stack: Current and caller frames, each frame keeping the state of Java (not native) method invocation:
    • Values of local variables
    • Method parameters values
    • Values of operands for intermediate calculations (operand stack)
    • Method return value (if any)
  • Program Counter (PC) register: Next instruction to execute
  • Native method stack: The state of native method invocations

We have already discussed that a programmer has to be careful while using reference types to not modify the object itself...