jdk vs jre vs jvm

This entry is part 2 of 34 in the series Core Java Course

Let’s start by defining JDK (Java Development Kit), JRE (Java Runtime Environment), and JVM (Java Virtual Machine).

JDK (Java Development Kit)

JDK contains everything that will be required to develop and run Java application.

JRE (Java Run time Environment)

JRE contains everything required to run Java application which has already been compiled. It doesn’t contain the code library required to develop Java application.

JVM (Java Virtual Machine)

JVM is a virtual machine which work on top of your operating system to provide a recommended environment for your compiled Java code. JVM only works with bytecode. Hence you need to compile your Java application(.java) so that it can be converted to bytecode format (also known as the .class file). Which then will be used by JVM to run application. JVM only provide the environment It needs the Java code library to run applications.

JDK vs JRE vs JVM

The below chart shows the different features of each of the Java technologies.

JDK_JRE_JVM

*Image Courtesy : Oracle Corporation

Now as per diagram you can identify what is the difference.

JRE = JVM + Required Library to run Application.

JDK = JRE + Required Library to develop Java Application.

Java Portability

In order to understand portability in Java you need to understand what happens to java code from start to finish.

1- Java Source Code (Written by Developer) (Machine Neutral)

2- Compiled Code / Byte Code (Compiled by javac) . (Machine Neutral)

3- Byte Code executed (Executed by JVM) (Machine Specific)

In step 2, javac (Java Compiler) converts Java code to byte code. This can be moved to any machine(Windows / Linux) and executed by JVM. JVM reads the bytecode and generates machine specific code. In order to generate machine specific code JVM needs to be machine specific. So every type of Machine(Windows / Linux / Mac) has a specific JVM. So in this way the coder doesn’t need to bother with generating byte code. JVM takes care of portability. So the final answer is Java is Portable but JVM is Machine Specific.

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28 Comments jdk vs jre vs jvm

  1. loku

    This is a great article to know the basics differences between all these three main terms. Liked it. Keep going on!!

    Reply
  2. Vijay G

    It is very simple but explains crystal clear about the basics of jdk, jre and jvm… Anyone can understand so easily…

    Reply
  3. Nandu

    Hi,

    I am very new beginner for java…This is very nice tutorial.

    I need some clarification reg JDK,JRE and JVM

    As you said, JRE is combination of specific libraries(math and util) and JVM,

    For a simple HELLO WORLD program ,will javac and JVM be enough to compile and get the result as there is no use of specific libraries in evaluating the result?

    Cheers,
    Nandu

    Reply
    1. J Singh

      Hi Nandu,

      Sorry for late reply. As per your question it might look like you only need only javac and JVM. But truth is even if you don’t import any library there are some libraries which will be imported implicitly. and you will require some basic libraries even for simplest application.
      Hope it clarifies.

      Regards

      Reply
  4. avnika

    Nice to understand.. i would like to learn core java need online classes if possible to you can you please share your details

    Reply
  5. kashif

    Dear author,
    You’ve spent so much effort putting all this up, which can become even better with some editing, especially punctuation and sentence flow.
    it’s just a suggestion. Keep up the good work!

    Reply
    1. J Singh

      I do agree with you there are problems with articles. And we have just started working on that. We can’t revisit all old articles. But we are trying touch base and correct article as much as possible. Thanks for your suggestion though.

      Regards

      Reply

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