The Java Virtual Machine (JVM) is an abstract computing machine that executes Java bytecode. It has several core components including a class loader, memory areas like the heap and stack, and an execution engine. The execution engine initially interprets bytecode instructions but can optimize performance by just-in-time compiling frequently used bytecode into native machine code. The JVM provides a layer of abstraction between Java applications and the underlying hardware or operating system.

1. Java Virtual Machine

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What do
you mean by
JVM?
The abstract
specification
A concrete
implementation
A runtime
instance
What is a Java Virtual Machine?
JVM Overview

3. 3
JVM Structure
JVM Overview

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JVM Architecture
JVM Architecture

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Class Loader
Class Loader

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Class Loader Cont..
Class Loader

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Java Memory Area
Memory Management

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Java Memory Area Cont..
Memory Management

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PC Register
 Each thread of a running program has its own PC register
 PC register is created when the thread is started
 As a thread executes a Java method, PC register contains
the instruction currently being executed by the thread
Memory Management
Keeps track of the current instruction executing at any
moment

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JVM Stack
 Stack frame: One stack frame is created
whenever a method is executed in the
JVM, and the stack frame is added to
the JVM stack of the thread
 Local variable: The parameters sent to
the method are saved. After the
method parameters, the local variables
of the method are saved
Memory Management
 Operand stack: An actual workspace of a method. Each method exchanges data
between the Operand stack and the local variable array, and pushes or pops
other method invoke results

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Native method stack
 In other words, it is a stack used to execute C/C++ codes
invoked through JNI
 According to the language, a C stack or C++ stack is created
Memory Management
Stack for native code written in a
language other than Java

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Heap
Memory Management

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Heap
Memory Management

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Execution Engine
 Interpreter: Reads, interprets and
executes the bytecode instructions
one by one.
JVM Execution engine
 JIT compiler: The execution engine runs as an interpreter first, and at the
appropriate time, the JIT compiler compiles the entire byte code to
change it to native code

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Execution Engine - JIT Compiler
JVM Execution engine
 JIT compiler: The execution engine runs as an interpreter first, and at the
appropriate tie, the JIT compiler compiles the entire byte code to change
it to native code

16. Questions ???