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JRE and JDK for Java Platform

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JRE and JDK for Java Platform


If you are a Java programmer it’s very much important for you to have a better understanding of its Environment and basic concepts. So the very first thing which you should be knowing is, what is a JRE and JDK. While installing Java, you have to install these to make your application functional. But mostly people are not clear what the difference between these two is. So let’s discusses the major differences between JRE and JDK.


JRE(Java Runtime environment)

JDK(Java Development Kit)

It is an implementation of the “Java Virtual Machine” which actually executes Java programs.

It is a bundle of software that you can use to develop Java based applications.

Java Runtime Environment is a plug-in needed for running java programs. It is used to provide runtime environment.

Java Development Kit is needed for developing java applications.

It includes the JVM, Core libraries, browser plugins and other additional components to run applications and applets written in Java.

It includes the JRE, set of API classes, Java compiler (javac in its bin directory), tools (like JavaDoc, and Java Debugger) Webstart and additional files needed to write Java applets and applications.

The JRE is smaller than the JDK so it needs less Disk space.

The JDK needs more Disk space as it contains the JRE along with various development tools.




So, the conclusion is, when you only want to run Java programs on your browser or computer you will only install JRE. It's all you need. But, if you are planning to do some Java programming, you will also need JDK. Sometimes, even though 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 WebApp with JSP, you are technically just running Java Programs inside the application server and because application server will convert JSP into Servlets and use JDK to compile the servlets, you need JDK.

In mathematical language we can say that, 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. Typically, each JDK contains one (or more) JRE's along with the various development tools like the Java source compilers, bundling and deployment tools, debuggers, development libraries, etc.


Now the next very big question is, that if we have a JDK, do we still need to have JRE?


The answer is that, you don’t need to install JRE then because JDK usually consists of both development and run-time environments in it. Installing JDK will automatically install JRE.

So if you want to compile a program, i.e. javac <filename.java> you need to have JDK which already have JRE in it. But to do java <filename> you need only JRE, which is within JDK. Thus having latest JDK installed into your system, you don’t need JRE separately. So it depends on you what you want to do, whether just want to run java programs (then you only need JRE) or want to develop then also (then you need JDK).

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