(a) J.V.M (Java Virtual Machine)-
J.v.m = j.i.t(just-in-time compiler)+cache
-J.v.m Doesn’t exists physically,
-J.v.m provides specifications to execute java byte-code.
-J.v.m is platform dependent and easily available for many platforms(OS)
*JVM internal architecture*-
(b)JRE (Java Runtime Environment)-
– implementation of JVM.
– physically exists.
JRE = JVM + Set of libraries (i.e. jar) + Other Files
(c)JDK (Java Development Kit)-
– physically exists.
JDK = JRE + Development tools(i.e. javac, java etc)
Core Java in 25 hours 
you can consider jvm as a computer for which machinre language is bytecode .
And jre builds this virtiual computer (i.e jvm) on your machine(p.c) so it can run program .
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Sir can you plz elaborate some useful tools(Java,javaw,javap etc.) of jdk
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yes, of course…
Basic Tools
These tools are the foundation of the JDK. They are the tools you use to create and build applications.
1-javac The compiler for the Java programming language.
2-java The launcher for Java applications.
3-javadoc API documentation generator.
4-apt Annotation processing tool.
5-jar Create and manage Java Archive (JAR) files.
6-jdb The Java Debugger.
7-javap Class file disassembler
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