JAVA VIRTUAL MACHINEDhanith Krishna

Virtual Machines

A virtual machine (VM) is a software-based emulation of a computer.

JVM executes Java byte code

Byte code is one byte op-codes followed by optional parameters

JVM platform is used by Python, Ruby etc

code execution component of the Java platform

JVM Architecture

•Better Security

•Portability

•Compile Once Run Anywhere

NEED FOR JVM

IS JVM for JAVA alone ?

• Compilers for other languages based on JVM exists

• Assemblers on JVM

•Erjang

•Rhino

•Free Pascal

•Quercus

•Jython

•NetRexx

•Jruby

•Jacl

• Loads class to memory

• Verification

• Allocation of static fields

• Linking

• Invocation of initialization codes

• Starting Main as a single thread

• Additional Threads are created using Thread class

How class file works in JVM ?

JVM Architecture

Storage Management

Storage Management

Global Data – Global constant poolContains program constants and symbol table information

Per Thread Data – registers + stack + native stack

Heap – Dynamically allocated memory

Class File Format

JVM Instruction Set

•Load and store

•Arithmetic

•Type conversion

•Object creation and manipulation

•Operand stack management (push / pop)

•Control transfer (branching)

•Method invocation and return

•Throwing exceptions

•Monitor-based concurrency