Java Tutorial

OOPS concept


JVM - Java Virtual Machine

What is JVM?

JVM is an abstarct machine which provides runtime environment in which java byte code can be executed.
JVM is platform dependent and hence for every platform there is a different JVM.

Functions of JVM

JVM perform following functions:

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

    JVM Architecture

    Class Loader

    It loads the Class for execution.

    Method Area

    Stores pre-class structure as constant pool.


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


    Local variables and partial results are store here. Each thread has a private JVM stack created when the thread is created.

    Program Counter Register

    It contains the address of the Java virtual machine instruction currently being executed.

    Native Method Stack

    It contains all native used in application.

    Execution Engine

    Execution engine controls the execute of instructions contained in the methods of the classes.
    It contains: 1) A virtual processor 2) Interpreter 3) Just-In-Time(JIT) compiler

    Native Method Interface

    It provides an interface between Java code and native codes.

    Native Method Libraries

    It consists of files that are required for the execution of native code.