What is JRE, JVM, and JDK?

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Difference between JRE, JVM, and JDK
By ANONYO SANYAL

Now, this article lays a foundation to learn the internals of a JVM. To do that first we need to understand JRE, JVM and JDK and their differences. Once you are done click here to learn the internal details of JVM

JVM:-

Firstly JVM stands for Java Virtual Machine.  Secondly, JVM is an abstract machine i.e. it doesn't exist in reality. It is just an abstract concept. It is the detailed description of the design and materials which provides a runtime environment to run the java bytecode. 
Funny fact, we all know java is a platform independent programming language. But do you know that JVM, JRE, and JDK are platform dependent? The reason is pretty clear. we said that JVM gives a specification (detailed description of the design and materials) for the runtime environment to run the java bytecode. But the specification changes from one Operating System to another. Now to make Java a platform-independent programming language this step had to be taken. Otherwise, say for example JRE, JVM and JDK were built only for Linux systems. Then windows user could never run a java application. Then, in that case, Java would not be platform independent.
Now coming back to JVM, it's main four functions are:-
  1. Loads code
  2. Verifies code
  3. executes code
  4. Provides runtime environment

 JRE:- 

JRE stands for Java Runtime Environment. It is sometimes also called Java RTE. It is basically an implementation of JVM. Unlike JVM it physically exists.
The Java Runtime Environment is a set of software tools that are extensively used to make Java Applications of various types. It is mainly used to provide the running environment commonly known as runtime environment.JRE consists of JVM, some libraries and some external miscellaneous files that are needed by the JVM to run the application. The schematic block diagram of JRE is given below. 
JRE schematic block diagram
JRE is released by Sun Microsystems

JDK:-

JDK is short for Java Development Kit. JDK is a software development environment which is used to make various java applications. JDK is basically development tools added on to JRE. 
JDK is the implementation of either of the following platforms released by Oracle Corporation.
  • SE(Standard Edition) Java Platform
  • EE(Enterprise Edition) Java Platform
  • ME(Micro Edition) Java Platform
The scheme of JDK is given below.
    Scheme of JDK
    Thus we can conclude that JVM is the heart of everything. Therefore it is important to learn the details of JVM.

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