What is the difference between JDK and JRE

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What is the difference between JDK and JRE   What are their roles and when should I use one or the other

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Here s a simple response directly from Oracle http   docs oracle com javase 7 docs technotes guides   Java SE Runtime Environment  JRE   The JRE provides the libraries  Java virtual machine  and other components necessary for you to run applets and applications written in the Java programming language  This runtime environment can be redistributed with applications to make them free-standing   Java SE Development Kit  JDK   The JDK includes the JRE plus command-line development tools such as compilers and debuggers that are necessary or useful for developing applets and applications

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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      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  JVM  JRE   and JDK are platform dependent because configuration of each OS   differs  But  Java is platform independent       JRE      It contains everything you need to run Java applications in compiled   form  You don t need any libraries and other stuffs  All things you   need are compiled       JRE is can not used for development  only used for run the   applications       Java SE Development Kit  JDK       The JDK includes the JRE plus command-line development tools such as   compilers and debuggers that are necessary or useful for developing   applets and applications     Sources  GeeksForGeeks Q amp A  Java Platform Overview

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jdk is necessary to compile to code and convert java code to byte codes while jre is necessary for executing the byte codes

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If you want to run Java programs  but not develop them  download the Java Run-time Environment  or JRE  If you want to develop them  download the Java Development kit  or JDK  JDK  Let s called JDK is a kit  which include what are those things need to developed and run java applications    JDK is given as development environment for building applications  component s and applets    JRE  It contains everything you need to run Java applications in compiled form  You don t need any libraries and other stuffs  All things you need are compiled    JRE is can not used for development  only used for run the applications

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The difference between JDK and JRE is that JDK is the software development kit for java while JRE is the place where you run your programs

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JVM  Java Virtual Machine  is an abstract machine  It is a specification that provides runtime environment in which java bytecode can be executed   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 is an acronym for Java Development Kit It physically exists It contains JRE   development tools

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The answer above  by Pablo  is very right  This is just additional information   The JRE is  as the name implies  an environment  It s basically a bunch of directories with Java-related files  to wit    bin  contains Java s executable programs  The most important is java  and for Windows  javaw as well   which launches the JVM  There are some other utilities here as well  such as keytool and policytool  conf  holds user-editable configuration files for Java experts to play with  lib  has a large number of supporting files  some  jars  configuration files  property files  fonts  translations  certs  etc      all the  trimmings  of Java  The most important is modules  a file that contains the  class files of the Java standard library  At a certain level  the Java standard library needs to call into native code  For this purpose  the JRE contains some  dll  Windows  or  dylib  macOS  or  so  Linux  files under bin  or lib  with supporting  system-specific native binary code    The JDK is also a set of directories  It is a superset of the JRE  with some additions    bin  has been enlarged with development tools  The most important of them is javac  others include jar  javadoc and jshell  jmods   which holds JMOD files for the standard library  has been added  These files allow the standard library to be used with jlink

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Simply     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 documentation

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JDK is a superset of JRE  and contains everything that is in JRE  plus tools such as the compilers and debuggers necessary for developing applets and applications  JRE provides the libraries  the Java Virtual Machine  JVM   and other components to run applets and applications written in the Java programming language

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In layman terms  JDK is grandfather JRE is father and JVM is their son   i e   JDK  gt  JRE  gt  JVM    JDK   JRE   Development debugging tools JRE   JVM   Java Packages Classes like util  math  lang  awt swing etc  runtime libraries  JVM   Class loader system   runtime data area   Execution Engine   In other words 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  JVM   The Java Virtual Machine  JVM  is the virtual machine that run the Java bytecodes  The JVM doesn t understand Java source code  that s why you compile your   java files to obtain   class files that contain the bytecodes understandable 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 JDK  JIT Compile Process  Courtesy  Oracle documentation

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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   Implementation of JVMs are also actively released by other companies besides Sun Micro Systems     JDK  JDK is an acronym for Java Development Kit It physically exists It contains JRE   development tools

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JVM  JRE  JDK - these are all the backbone of Java language  Each component work separately  JDK and JRE physically exist but JVM is an abstract machine that means it does not physically exist   JVM is the subsystem of JDK and JRE which is used to check the intermediate code known as  bytecode   It first loads the  class file   having  c extension  generated by the Java compiler  javac  through JVM subsystem classloader and classified memory location  class area  stack  heap and pc registers  according to their use  Then it checks all the bytecode to ensure that it is returned in Java and all memory accessibility access by the network  The interpreter s work starts after that where it checks the whole program line by line  The results are finally shown in the console browser application through JRE  Java Runtime Environment  which runtime facilities   JRE is also a subsystem of JDK which provides runtime facilities like JVM  classes  executable files like  jar file  etc   JDK stands for Java Development Kit  It contains all necessary components used in Java programming such as class  method  swing  AWT  package  Java  interpreter   javac  compiler   appletviewer  applet application viewer   etc  To conclude  it contains every file required for developing applications  whether standalone or web-based

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A clear understanding of these terms JVM  JDK  JRE  are essential to grasp their usage and differences   JVM Java Virtual Machine  JVM  is a run-time system that executes Java bytecode  The JVM is like a virtual computer that can execute a set of compiled instructions and manipulate memory locations  When a Java compiler compiles source code  it generates a highly optimized set of instructions called bytecode in a  class file  The JVM interprets these bytecode instructions and converts them to machine-specific code for execution   JDK The Java Development Kit  JDK  is a software development environment that you can use to develop and execute Java applications  It includes the JRE and a set of programming tools  such as a Java compiler  interpreter  appletviewer  and document viewer  The JDK is implemented through the Java SE  Java EE  or Java ME platforms    JRE The Java Runtime Environment  JRE  is a part of the JDK that includes a JVM  core classes  and several libraries that support application development  Though the JRE is available as part of the JDK  you can also download and use it separately   For complete understanding you can see my Blog   Jdk Jre Jvm and differences

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The JRE is the Java Runtime Environment  It is a package of everything necessary to run a compiled Java program  including the Java Virtual Machine  JVM   the Java Class Library  the java command  and other infrastructure  However  it cannot be used to create new programs   The JDK is the Java Development Kit  the full-featured SDK for Java  It has everything the JRE has  but also the compiler  javac  and tools  like javadoc and jdb   It is capable of creating and compiling programs   Usually  if you only care about running Java programs on computer you will only install the JRE  It s all you need  On the other hand  if you are planning to do some Java programming  you need to install the JDK instead    Sometimes  even if you are not planning to do any Java development on a computer  you still need the JDK installed  For example  if you are deploying a web application with JSP  you are technically just running Java programs inside the application server  Why would you need the JDK then  Because the application server will convert JSP into Java servlets and needs to use the JDK to compile the servlets  I am sure that there are more examples

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From Official java website     JRE   Java Runtime environment     It is an implementation of the Java Virtual Machine  which actually executes Java programs  Java Runtime Environment is a plug-in needed for running java programs  The JRE is smaller than the JDK so it needs less Disk space  The JRE can be downloaded supported freely from https   www java com It includes the JVM   Core libraries and other additional components to run applications and applets written in Java    JDK  Java Development Kit    It is a bundle of software that you can use to develop Java based applications  Java Development Kit is needed for developing java applications  The JDK needs more Disk space as it contains the JRE along with various development tools  The JDK can be downloaded supported freely from https   www oracle com technetwork java javase downloads  It includes the JRE  set of API classes  Java compiler  Webstart and additional files needed to write Java applets and applications

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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  Usually  when you only care about running Java programs on your browser or computer you will only install JRE  It s all you need  On the other hand  if you are planning to do some Java programming  you will also need JDK

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JDK includes the JRE plus command-line development tools such as compilers and debuggers that are necessary or useful for developing applets and applications   JRE is basically the Java Virtual Machine where your Java programs run on  It also includes browser plugins for Applet execution   JDK is an abstract machine  It is a specification that provides runtime environment in which java bytecode can be executed   So  Basically JVM  lt  JRE  lt  JDK as per  Jaimin Patel said

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One difference from a debugging perspective   To debug into Java system classes such as String and ArrayList  you need a special version of the JRE which is compiled with  debug information   The JRE included inside the JDK provides this info  but the regular JRE does not  Regular JRE does not include this info to ensure better performance   What is debugging information  Here is a quick explanation taken from this blog post      Modern compilers do a pretty good job converting your high-level code  with its nicely indented and nested control structures and arbitrarily typed variables into a big pile of bits called machine code  or bytecode in case of Java   the sole purpose of which is to run as fast as possible on the target CPU  virtual CPU of your JVM   Java code gets converted into several machine code instructions  Variables are shoved all over the place     into the stack  into registers  or completely optimized away  Structures and objects don   t even exist in the resulting code     they   re merely an abstraction    that gets translated to hard-coded offsets into memory buffers       So how does a debugger know where to stop when you ask it to break at the entry to some function  How does it manage to find what to show you when you ask it for the value of a variable     The answer is     debugging information       Debugging information is generated by the compiler together with the machine code  It is a representation of the relationship between the executable program and the original source code  This information is encoded into a pre-defined format and stored alongside the machine code  Many such formats were invented over the years for different platforms and executable files

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suppose  if you are a developer then your role is to develop program as well as to execute the program  so you must have environment for developing and executing  which is provided by JDK   suppose  if you are a client then you don t have to worry about developing Just you need is  an environment to run program and get result only  which is provided by JRE   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  JRE and JDK are platform dependent because configuration of each OS differs  But  Java is platform independent    Java Virtual Machine  JVM  is a run-time system that executes Java bytecode    JRE is the environment  standard libraries and JVM  required to run Java applications   The JDK includes the JRE plus command-line development tools such as compilers and debuggers that are necessary or useful for developing applets and applications

[java] What is the difference between JDK and JRE?

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