Thursday, December 29, 2011

Difference between JRE JVM and JDK in Java Programming language

JRE, JVM and JDK are three terms you often heard in conjunction with Java programming language and most people either confuse between them or think they all are same. In this java article we will what is Java Run-time (JRE), what is Java virtual Machine (JVM) and what is Java development Kit (JDK) along with Just in Time compiler or JIT. Once you know what JRE, JVM or JDK means you can differentiate them easily by yourself.  This article is in continuation of Difference between Comparable and Comparator in Java and Difference between ConcurrentHashMap and Synchronized-map.

JRE JVM and JDK in Java Programming language

Java Runtime Environment (JRE)

Difference between JVM JRE and JDK in Java Programming languageJava is every where in browser, in mobile, in TV or in set-top boxes and if you are into Java programming language than you know that Java code which is bundled in JAR (Java archive) file require Java virtual machine JVM to execute it. Now JVM is an executable or program like any other program and you can install that into your machine. You have seen browser often suggesting download JRE to run a Java Applet downloaded from Internet. Various version of JRE are available in java.oracle.com and most of the user who just want to execute Java program inside browser or standalone downloads JRE. All browsers including Internet Explorer, Firefox and Chrome can work with JRE.

Java Virtual Machine (JVM)

When you download JRE and install on your machine you got all the code required to create JVM. Java Virtual Machine is get created when you run a java program using java command e.g. java HelloWorld. JVM is responsible for converting byte code into machine specific code and that's why you have different JVM for Windows, Linux or Solaris but one JAR can run on all this operating system. Java Virtual machine is at heart of Java programming language and provide several feature to Java programmer including Memory Management and Garbage Collection, Security and other system level services. Java Virtual Machine can be customized e.g we can specify starting memory or maximum memory of heap size located inside JVM at the time of JVM creation. If we supplied invalid argument to java command it may refuse to create Java Virtual Machine by saying "failed to create Java virtual machine: invalid argument". In short Java Virtual Machine or JVM is the one who provides Platform independence to Java.

Java Development Kit (JDK)

JDK is also loosely referred as JRE but its lot more than JRE and it provides all the tools and executable require to compile debug and execute Java Program. Just like JRE, JDK is also platform specific and you need to use separate installer for installing JDK on Linux and Windows. Current Version of JDK is 1.7 which is also referred as Java7 and it contains javac (java compiler) based on programming rules of Java7 and Java which can execute java7 code with new features like String in Switch, fork-join framework or Automatic Resource Management. When you install JDK, installation folder is often referred as JAVA_HOME. All binaries are located inside JAVA_HOME/bin which includes javac, java and other binaries and they must be in your system PATH in order to compile and execute Java programs. For details on Path see how to set PATH for Java in Windows and UNIX.

Difference between JRE, JDK and JVM

In short here are few differences between JRE, JDK and JVM:

1)  JRE and JDK come as installer while JVM are bundled with them.
2)  JRE only contain environment to execute java program but doesn’t contain other tool for compiling java program.
3)  JVM comes along with both JDK and JRE and created when you execute Java program by giving “java” command.

Just in Time Compiler (JIT)

Initially Java has been accused of poor performance because it’s both compiles and interpret instruction. Since compilation or Java file to class file is independent of execution of Java program do not confuse. Here compilation word is used for byte code to machine instruction translation. JIT are advanced part of Java Virtual machine which optimize byte code to machine instruction conversion part by compiling similar byte codes at same time and thus reducing overall execution time. JIT is part of Java Virtual Machine and also performs several other optimizations such as in-lining function.

That’s all on JRE, JDK and Java Virtual machine and difference between them. Though they look similar they are different and having a clear idea of JVM, JIT or JDK helps in java programming.

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11 comments :

JDK Guru said...

Another differnce over JDK vs JRE is that when you install JDK in your machine , JRE comes automatically and you can check this by going to your JAVA_HOME or Java installation directory. JRE should be in PATH JAVA_HOME/jre. Also all certificates used by Java are stored in keystore which exists inside JRE folder.

Anonymous said...

Can we run Java program without JRE? does JRE only contains java or javaw command or something else ?

Nitin Jain said...

If JVM is platform independent then why JVM is different for Windows and Linux?

amit said...

I Couldn't understand the JIT part.

Anonymous said...

I came to know that jvm is not a program it is just doccumentation containing specifications on what should be the format of exe etc.jre is responsible for the execution of java program .

Anonymous said...

Amit
Every program need to satisfy the security policies after loading till execution. this affected the execution speed .jit is both compiler and interpreter used to compensate this loss.most of the compiler now are jit.

Elangovan M said...

which is platform independent JDK or JRE

Anonymous said...

JRE : jre contains the jvm and some other libraries and file which is helpful for jvm to execute the java program.

JDK : jdk contains JRE and Development tools like javac ,java etc

Shubham said...

To Nitin Jain. JVM is not platform independent, Java is platform independent. In-fact JVM creates a environment, so that Java could be platform independent. JVM is according to platforms like windows/linux/Mac. A .class file of a .java file could be executed on any JVM, and it gives same result on each platform (thus platform independence). actually the Machine code (of this .class file) which is generated by JVM is according platform.

Shubham said...

To Amit : In java, code is interpreted i.e. converted line by line. While in compilation whole code is converted in a go. But Java also support JIT compilation, in which a common chunk of code which is repetitively used, can be compiled once and placed at some place. Now rest of the Java code is interpreted, and when call comes to repetitive part, the compiled code is used (instead of interpreting the part again). You can relate it with a Loop, where code related to loop is compiled separately, and this compiled code is referred when call comes to loop, instead to interpreting the code related to loop n times.

Anonymous said...

To Amit: In short words, what is platform independant is the java bytecode
JVM need to be platform specific because it will translate this bytecode into machine code.
As Shubham said, for example if you write your program in Windows and you create your .class, then this .class file is platform independant, the hosting JVM (let´s give another example here, let´s say we have as destiny a client with a JVM in Linux and other client in Solaris, well you don´t need to recompile your code again and again, the given JVM will know what this .class bytecode means so then the given JVM will translate your code into the given machine code, that´s it

hopes this helps :)

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