What is the difference between JVM JDK JRE OpenJDK

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What is the difference between JVM  JDK  JRE  amp  OpenJDK   I was programming in Java and I encountered these phrases  what are the differences among them

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In summary     JRE   JVM   Java Packages  like util  math  lang  awt  swing etc    runtime libraries JDK   JRE   Development debugging tools   If you want to develop in java  you need the JDK  but if you just want run java  you need the JRE

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JRE executes the application but JVM reads the instructions line by line so it s interpreter   JDK JRE Development Tools  JRE JVM Library Classes

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JVM   A specification which describes the the way resources to run a java program  Actually executes the byte code and make java platform independent  In doing so  it is different for different platform  JVM for windows cannot work as JVM for UNIX   JRE   Implementation of JVM   JVM   run time libraries   JDK   JRE   java compiler and other essential tools to build a java program from scratch

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In layman terms - JDK   JRE   Development debugging tools  where JDK is our complete package to work with Java  from creating compiling till running it On the other hand JRE is just of running of code Byte Code    Note - Whether we are installing JDK or JRE  JVM would come bundled with both the packages and JVM is the part where JIT compiler converts the byte code into the machine specific code   Just read the article on JDK JRE  JVM and JIT

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JVM Java Virtual Machine   actually executes the java bytecode  It is the execution block on the JAVA platform  It converts the bytecode to the machine code   JRE Java Runtime Environment   provides the minimum requirements for executing a Java application  it consists of the Java Virtual Machine  JVM   core classes  and supporting files   JDK Java Development Kit  it has all the tools to develop your application software  It is as JRE JVM  Open JDK  is a free and open source implementation of the Java Platform

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JDK  Java Development Kit   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 is targeted for execution of Java files  i e  JRE   JVM   Java Packages Classes like util  math  lang  awt swing etc  runtime libraries   JDK is mainly targeted for java development  I e  You can create a Java file  with the help of Java packages   compile a Java file and run a java file   JRE  Java Runtime Environment   Java Runtime Environment contains JVM  class libraries  and other supporting files  It does not contain any development tools such as compiler  debugger  etc  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  The Java Virtual Machine provides a platform-independent way of executing code  That mean compile once in any machine and run it any where any machine    JVM  Java Virtual Machine   As we all aware when we compile a Java file  output is not an    exe    but it   s a     class    file      class    file consists of Java byte codes which are understandable by JVM  Java Virtual Machine interprets the byte code 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   There are different JVM implementations are there  These may differ in things like performance  reliability  speed  etc  These implementations will differ in those areas where Java specification doesn   t mention how to implement the features  like how the garbage collection process works is JVM dependent  Java spec doesn   t define any specific way to do this

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Java is the language and includes a strict and strongly typed syntax with which you should be very familiar by now   Java 2 Platform  Standard Edition  also known as J2SE  referred to the platform and included the classes in the java lang and java io packages  among others  It was the building block that Java applications were built upon   A Java Virtual Machine  or JVM  is a software virtual machine that runs compiled Java code  Because compiled Java code is merely bytecode  the JVM is responsible for compiling that bytecode to machine code before running it   This is often called the Just In Time Compiler or JIT Compiler   The JVM also takes care of memory management so that application code doesn   t have to   The Java Development Kit  or JDK  was and remains the piece of software Java developers use to create Java applications  It contains a Java language compiler  a documentation generator  tools for working with native code  and  typically  the Java source code for the platform to enable debugging platform classes   The Java Runtime Environment  or JRE  was and remains the piece of software end users download to run compiled Java applications  It includes a JVM but does not contain any of the development tools bundled in the JDK  The JDK  however  does contain a JRE

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JVM is abbreviated as  Java Virtual Machine  JVM is the main component of java architecture  JVM is written in C programming language  Java compiler produce the byte code for  JVM   JVM reading the byte code  verifying the byte code and linking the code with the ibrary  JRE is abbreviated as Java Runtime Environment  it is provide environment at runtime  It is physically exist  It contain  JVM   set of libraries jar   other files  JDK is abbreviated as  Java Development Kit   it is develop java applications  And also Debugging and monitoring java applications   JDK contain JRE  development tools javac java   OpenJDK  OpenJDK is an open source version of sun JDK  Oracle JDK is Sun s official JDK

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JDK - Compiles java to ByteCode  Consists of debuggers  Compilers etc   javac file java    Is executed using JDK   JVM - Executes the byte code  JVM is the one which makes java platform independent  But JVM varies for platforms   JRE - JVM along with java runtime libraries to execute java programs

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Another aspect worth mentioning   JDK  java development kit    You will need it for development purposes like the name suggests   For example  a software company will have JDK install in their computer because they will need to develop new software which involves compiling and running their Java programs as well   So we can say that JDK   JRE   JVM   JRE  java run-time environment   It s needed to run Java programs  You can t compile Java programs with it     For example  a regular computer user who wants to run some online games then will need JRE in his system to run Java programs   JVM  java virtual machine    As you might know it run the bytecodes  It make Java platform independent because it executes the  class file which you get after you compile the Java program regardless of whether you compile it on Windows  Mac or Linux   Open JDK  Well  like I said above  Now JDK is made by different company  one of them which happens to be an open source and free for public use is OpenJDK  while some others are Oracle Corporation s JRockit JDK or IBM JDK   However they all might appear the same to general user   Conclusion   If you are a Java programmer you will need JDK in your system and this package will include JRE and JVM as well but if you are normal user who like to play online games then you will only need JRE and this package will not have JDK in it   In other words JDK is grandfather JRE is father and JVM is their son

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JVM The Java Virtual Machine  JVM  is the virtual machine that runs the Java bytecodes  The JVM doesn t understand Java source code  that s why you need compile your   java files to obtain   class files that contain the bytecodes understood by the JVM  It s also the entity that allows Java to be a  quot portable language quot   write once  run anywhere   Indeed  there are specific implementations of the JVM for different systems  Windows  Linux  macOS  see the Wikipedia list   the aim is that with the same bytecodes they all give the same results  JDK and JRE To explain the difference between JDK and JRE  the best is to read the Oracle documentation and consult the diagram   Java Runtime Environment  JRE  The Java Runtime Environment  JRE  provides the libraries  the Java Virtual Machine  and other components to run applets and applications written in the Java programming language  In addition  two key deployment technologies are part of the JRE  Java Plug-in  which enables applets to run in popular browsers  and Java Web Start  which deploys standalone applications over a network  It is also the foundation for the technologies in the Java 2 Platform  Enterprise Edition  J2EE  for enterprise software development and deployment  The JRE does not contain tools and utilities such as compilers or debuggers for developing applets and applications  Java Development Kit  JDK  The JDK is a superset of the JRE  and contains everything that is in the JRE  plus tools such as the compilers and debuggers necessary for developing applets and applications   Note that Oracle is not the only one to provide JDKs  OpenJDK OpenJDK is an open-source implementation of the JDK and the base for the Oracle JDK  There is almost no difference between the Oracle JDK and the OpenJDK  The differences are stated in this blog   Q  What is the difference between the source code found in the OpenJDK repository  and the code you use to build the Oracle JDK  A  It is very close - our build process for Oracle JDK releases builds on OpenJDK 7 by adding just a couple of pieces  like the deployment code  which includes Oracle s implementation of the Java Plugin and Java WebStart  as well as some closed source third party components like a graphics rasterizer  some open source third party components  like Rhino  and a few bits and pieces here and there  like additional documentation or third party fonts  Moving forward  our intent is to open source all pieces of the Oracle JDK except those that we consider commercial features such as JRockit Mission Control  not yet available in Oracle JDK   and replace encumbered third party components with open source alternatives to achieve closer parity between the code bases   Update for JDK 11 - An article from Donald Smith try to disambiguate the difference between Oracle JDK and Oracle s OpenJDK   https   blogs oracle com java-platform-group oracle-jdk-releases-for-java-11-and-later

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JVM   this actually means the byte code interpreter  It is platform dependent  For eg  in      Windows platform the  java exe  or  javaw exe  precess is the jvm process   JDK   is a toolkit containing necessary libraries and utilities to develop and execute java program application  JRE  is the execution environment for a java application ie  it only support runtime dependencies including jvm for compiled program  If we want to compile a java program we need jdk

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JVM is the Java Virtual Machine     it actually runs Java ByteCode   JRE is the Java Runtime Environment     it contains a JVM  among other things  and is what you need to run a Java program   JDK is the Java Development Kit     it is the JRE  but with javac  which is what you need to compile Java source code  and other programming tools added   OpenJDK is a specific JDK implementation

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JDK  Java Development Kit      contains tools needed to develop the Java programs  You need JDK  if at all you want to write your own programs  and to compile them   JDK is mainly targeted for java development    JRE  Java Runtime Environment   Java Runtime Environment contains JVM  class libraries  and other supporting files  JRE is targeted for execution of Java files   JVM  Java Virtual Machine   The JVM interprets the byte code 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    Java Virtual Machine provides a platform-independent way of executing code

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JVM  JVM  Java Virtual Machine  is an abstract machine  It is a specification that provides runtime environment in which java bytecode can be executed  JVMs are available for many hardware and software platforms    JRE  JRE is an acronym for Java Runtime Environment It is used to provide runtime environment It is the implementation of JVM It physically exists It contains set of libraries   other files that JVM uses at runtime   JDK  JDK is an acronym for Java Development Kit It physically exists It contains JRE   development tools   Link  - http   www javatpoint com difference-between-jdk-jre-and-jvm

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JDK  The complete package which you need to write and run java code  OpenJDK  An independent implementation of JDK for making it much better  JVM  Converts Java code into bytecode and provides the specifications which tells how should a Java code be compiled  loaded  verified  checked for errors and executed   JRE  Implementation of the JVM with which some Java libraries are used to Run the program

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JVM   virtual machine of java  tells machine what to do with the Java Code  You cannot download JVM as is  It comes packaged in some other component   JRE  Some other component referred as above is the JRE   It is JVM  other jars to create runtime environmeny  JDK  contains JRE which in turn contains JVM   Once you get JDK you need not install JRE and JVM separately  It contains compiler which compiles your  java files to  class files

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A Java virtual machine  JVM  is a virtual machine that can execute Java ByteCode  It is the code execution component of the Java software platform   The Java Development Kit  JDK  is an Oracle Corporation product aimed at Java developers  Since the introduction of Java  it has been by far the most widely used Java Software Development Kit  SDK    Java Runtime Environment  is also referred to as the Java Runtime  Runtime Environment  OpenJDK  Open Java Development Kit  is a free and open source implementation of the Java programming language  It is the result of an effort Sun Microsystems began in 2006  The implementation is licensed under the GNU General Public License  GPL  with a linking exception

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JVM is the virtual machine Java code executes on  JRE is the environment  standard libraries and JVM  required to run Java applications  JDK is the JRE with developer tools and documentations  OpenJDK is an open-source version of the JDK  unlike the common JDK owned by Oracle

[java] What is the difference between JVM, JDK, JRE & OpenJDK?

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