Internal Details of JVM.

What is JVM:-
                          JVM (Java Virtual Machine) is an abstract machine. It is a specification that provides runtime environment in which java bytecode can be executed.


What is does:-
     
 The JVM performs following operation:

• Loads code
• Verifies code
• Executes code
• Provides runtime environment

JVM provides definitions for the:

• Memory area
• Class file format
• Register set
• Garbage-collected heap
• Fatal error reporting etc.

Internal Architecture of JVM:-

   1) Classloader:-
    Classloader is a subsystem of JVM that is used to load class files.

   2) Class(Method) Area:-

    Class(Method) Area stores per-class structures such as the runtime constant pool, 

    field and method data, the code for methods.
   3) Heap

    It is the runtime data area in which objects are allocated.
   4) Stack

    Java Stack stores frames.It holds local variables and partial results, and plays 

    a part in method invocation and return.

    Each thread has a private JVM stack, created at the same time as thread.
    A new frame is created each time a method is invoked. A frame is destroyed when 

    its method invocation completes.

   5) Program Counter Register

    PC (program counter) register. It contains the address of the Java virtual machine 

    instruction currently being executed.

   6) Native Method Stack

    It contains all the native methods used in the application.
   7) Execution Engine

    It contains:

     1) A virtual processor

     2) Interpreter: Read bytecode stream then execute the instructions.

     3) Just-In-Time(JIT) compiler: It is used to improve the performance.JIT compiles 

        parts of the byte code that have similar functionality at the same time, and 

        hence reduces the amount of time needed for compilation.Here the term ?

        compiler? refers to a translator from the instruction set of a Java virtual 

        machine (JVM) to the instruction set of a specific CPU.