JVM is a virtual
machine or a program that provides run-time environment in which java byte code
can be executed. JVMs are available for many hardware and software platforms.
The use of the
same byte code for all JVMs on all platforms makes java platform independent.
Class loader subsystem
Class loader
subsystem will load the .class file into java stack and later sufficient
memory will be allocated for all the properties of the java program into
following five memory locations
• Heap area
• Method area
• Java stack
• PC register
• Native stack
Heap area:
In which object
references will be stored.
Method area
In which static
variables non-static and static method will be stored.
Java Stack
In which all the
non-static variable of class will be stored and whose address referred by
object reference.
Pc Register
Which holds the
address of next executable instruction that means that use the priority for the
method in the execution process?
Native Stack
Native stack
holds the instruction of native code (other than java code) native stack
depends on native library. Native interface will access interface between
native stack and native library.
Execution Engine
It is a part JVM
that uses Virtual processor (for execution).which contain interpreter (for
reading instructions) and JIT (Just in time) compiler (for performance
improvement) for executing the instructions.
How JVM is created
When JRE
installed on your machine, you got all required code to create JVM. JVM is
created when you run a java program.
Lifetime of JVM
When an
application starts, a runtime instance is created.
When application
ends, runtime environment destroyed.
If “n”no.
of applications starts on one machine then “n” no. of runtime instances
are created and every application run on its own JVM instance.
Main task of JVM
1. Search and
locate the required files.
2. Convert byte
code into executable code.
3. Allocate the
memory into ram.
4. Execute the
code.
5. Delete the
executable code.
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