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Question about Eclipse, JDK, JVM and JRE


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#1 warnexus   Prime Members   -  Reputation: 1503

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Posted 15 February 2013 - 01:19 PM

I have a question about Eclipse, JDK, JRE and JVM. From what I understand so far.

 

 

Eclipse compiles your source code and runs your program

 

The JDK has a compiler called javac that turns your java source code into java byte code. 

 

JVM- a machine that acts like a real computer that runs your java byte code.

 

JRE- this is where all the available classes in the JAVA API is located in

 

In the event if a computer does not have the JVM, where does the user actually find one? Is the JVM in a processor chip or microprocessor because in wikiapedia, it said intel x86 jvm. So I was confused about this.

 

I'm sure this post will help people who are starting new to Java who questions why they need to install these things. happy.png 

 

 



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#2 Wyrframe   Members   -  Reputation: 733

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Posted 15 February 2013 - 02:09 PM

Eclipse; an editor and build-management environment.

 

JVM: Java Virtual Machine: the program, implemented differently for different platforms, that runs the java bytecode created by the compiler.

 

JRE: Java Runtime Environment. Usually the Oracle or GNU implementation. Contains a JVM and the standard library implementation, but no editors or compilers. It's meant to provide a complete but only sufficient runtime environment.

 

JDK: Java Development Kit: the JRE, plus a compiler.


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#3 __SKYe   Members   -  Reputation: 1098

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Posted 15 February 2013 - 02:10 PM

I'm not entirely sure about this, but i think this is correct:

 

Eclise is an IDE (Integration Developing(Developer) Environment. It has a text editor (where you code), sintax highlighting, etc.

 

JDK (Java Development Kit) - This is the Java equivalent to a SDK (Software Development Kit). It allows you to compile and create java programs into Java bytecode (.jar files).

You'd normally download this in conjunction with Eclipse or NetBeans (the IDEs normally allow you to download a bundle of IDE + JDK).

 

JRE (Java Runtime Environment) is needed fr running the JVM (Java Virtual Machine). Since Java is an interpreted language, it need the JVM to translate the Java bytecode into machine instructions (which can be x86, x86-64, PowerPC, etc). You can think of JRE being similar, in purpose, to Adobe Flash Player (without which you cannot play videos on the Youtube, etc).

 

If the user doesn't have the JRE, it can be downloaded for free in the Sun website (you just Google jre, and it will appear).

 

So JDK is only needed for who develops Java applications, and JRE is needed to run them.

 

Hope it helps.



#4 warnexus   Prime Members   -  Reputation: 1503

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Posted 15 February 2013 - 05:03 PM

Eclipse; an editor and build-management environment.

 

JVM: Java Virtual Machine: the program, implemented differently for different platforms, that runs the java bytecode created by the compiler.

 

JRE: Java Runtime Environment. Usually the Oracle or GNU implementation. Contains a JVM and the standard library implementation, but no editors or compilers. It's meant to provide a complete but only sufficient runtime environment.

 

JDK: Java Development Kit: the JRE, plus a compiler.

Thanks for the explanation. rolleyes.gif



#5 TheChubu   Crossbones+   -  Reputation: 4761

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Posted 15 February 2013 - 08:11 PM

The "byte code" is called an intermediary code between the source and the code that will get executed in your computer.

 

Your code gets translated to this intermediate language that the Java Virtual Machine understands. Its kinda a pseudo assembler, but instead of having x86 instructions, you have instructions for the JVM (think of it as a virtual processor which runs on top of your CPU).

 

The difference is that while assembly is compiled into an executable and runs directly on the CPU, the java byte code gets executed by the JVM. So this JVM translates the byte code into something the CPU in your computer can understand.

 

While on conventional languages you'd be compiling a separate executable for each architecture you're targeting (ie, one for x86, other for x86_64, etc), with managed languages (Java, C#, etc) you compile all the programs for a single target, the Virtual Machine, so you don't have to worry about the actual architecture which your program might get run on. Often you don't even have to worry about which OS your program gets run on either since developers try to abstract OS API specific calls in the standard libraries (say, you don't have to know how to create a window in Windows/OSX/Linux to create a window using Swing in Java).

 

The JVM does needs to be architecture specific since its the program in charge of actually running your Java bytecode in the environment of the user (CPU+OS). So you can't use a JVM for powerpc in a x86 CPU. The user has to install a working JVM to use your program (and any other program compiled for the JVM).

 

That's probably the main selling point of it. But as always, things aren't that simple and there are many ups and downs about using managed vs conventional languages. So beware of "what is better? C# or C++?" kind of questions because there isn't a simple all-encompassing answer for such things.


Edited by TheChubu, 15 February 2013 - 08:16 PM.

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#6 Aldacron   GDNet+   -  Reputation: 3273

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Posted 15 February 2013 - 09:38 PM

JDK (Java Development Kit) - This is the Java equivalent to a SDK (Software Development Kit). It allows you to compile and create java programs into Java bytecode (.jar files).
You'd normally download this in conjunction with Eclipse or NetBeans (the IDEs normally allow you to download a bundle of IDE + JDK).

 

That's almost correct. The JDK is the *official* sdk. There are other packages out there that are not the JDK, but that allow you to develop java programs. And Eclipse does not use the JDK. It ships with its own compiler. It does, however, require the JRE be installed on the system.






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