Answer Posted / pradeep panwar(sse)

JDK: Java Developer Kit contains tools needed to develop
the Java programs, and JRE to run the programs. The tools
include compiler (javac.exe), Java application launcher
(java.exe), Appletviewer, etc…

Compiler converts java code into byte code. Java
application launcher opens a JRE, loads the class, and
invokes its main method.

You need JDK, if at all you want to write your own
programs, and to compile them. For running java programs,
JRE is sufficient.

JRE: Java Runtime Environment contains JVM, class
libraries, and other supporting files. Actually JVM runs
the program, and it uses the class libraries, and other
supporting files provided in JRE. If you want to run any
java program, you need to have JRE installed in the system.

JVM: Java Virtual Machine interprets the bytecode into the
machine code depending upon the underlying operating system
and hardware combination. It is responsible for all the
things like garbage collection, array bounds checking, etc…
JVM is platform dependent.

The JVM is called "virtual" because it provides a machine
interface that does not depend on the underlying operating
system and machine hardware architecture. This independence
from hardware and operating system is a cornerstone of the
write-once run-anywhere value of Java programs.

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