Building projects with the JRE (not the JDK) in Eclipse

[zachwong]

Hi,

Just curious. I noticed in the Eclipse documentation the following:

By default, the JRE used to run the workbench will be used to build and run Java programs. It should appear with a checkmark in the list of installed JREs. We recommend that you use a Java SDK instead of a JRE. An SDK is designed for development and contains the source code for the Java library, easing debugging.

How does this work? Does this mean you can compile code with the JRE? My understanding is that you can only compile using "javac".

Any ideas?

Thanks

[Eranga]

I think you know about the meaning of two terminologies. JDK(Java Development Kit) and the JRE(Java Runtime Environment). As it said, you need JDK installed in your machine to develop Java applications. To run a Java application you need the runtime environment, you must.

Using JRE you can't develop any Java application. But if you have JDK installed then you can develop as well as run Java applications. That's JDK includes the JRE also.

Hope it's clear to you.

[zachwong]

Thanks for the quick reply!

I had the JRE1.6 installed when I first got my home computer (to run misc. Java apps on my home computer). In the JRE1.6 bin/ directory, there is no "javac" compiler.

I installed Eclipse today and was surprised to find that I was able to compile java code... despite the fact that the JRE is missing the java compiler.

To double check I didn't have a JDK installed on my computer, I did a search for "javac" and there was no results.

So I was just wondering how this could possibly be happening. Could Eclipse be using my compiler-less JRE1.6 to build code? Doesn't sound right, but I can't think of any otherway this is happening.

Thanks

[Eranga]

You said that, without having install the JDK package you can compile a Java project in Eclipse? But you can't run it? It can't happened, if you install JDK then there should be JRE too. B

By the way did you installed complete Eclipse package?

[zachwong]

I said that without having installed the JDK, and only having JRE1.6 installed, I can compile Java code in Eclipse. My thoughts are that if I don't have the JDK, then I shouldn't be able to build anything. Since I have a JRE, then I should be able to run it.

In my first post, I posted an excerpt from the Eclipse documentation. It sounds like you don't need a JDK, but you can compile with the JRE?

[Norm]

What program does eclipse use to compile java source?
It must include a JDK in its install.

The JRE doesn't include the javac and jar programs.

[zachwong]

It doesn't appear come with a JDK ... the prerequisite to run Eclipse is having either a JRE or JDK installed on the system.

I have JRE1.6 and despite having searched my system for the javac compiler, I couldn't find it... yet somehow... my small java test (Hello World) is still compiling.

[killua]

I have the same doubt with zachwong.
Only JRE installed, but eclipse is able to compile your java file.
After searching, I got a word "jrew". Someone said that jrew is another kind of binary version of javac and some other files contained in JDK.
And Eclipse uses this tool to compile java file without JDK installed.

[Eranga]

It doesn't appear come with a JDK ... the prerequisite to run Eclipse is having either a JRE or JDK installed on the system.

I have JRE1.6 and despite having searched my system for the javac compiler, I couldn't find it... yet somehow... my small java test (Hello World) is still compiling.

Never it can't happen. There should be JDK install. If you can't find that there should be another Java compiler. javac is not the only one we have. May be another one is attached to Eclipse. I'm not an Eclipse user, so I don't know that is possible or not.

[killua]

Never it can't happen. There should be JDK install. If you can't find that there should be another Java compiler. javac is not the only one we have. May be another one is attached to Eclipse. I'm not an Eclipse user, so I don't know that is possible or not.

I also believe that java can't be compiled without java compiler.
But the truth is that even you can't find javac in your computer, eclipse is still able to compile your java file.

So I think now the problem is that what is the SPECIFIC kind of compiler eclipse is using?

[Eranga]

I have the same doubt with zachwong.
Only JRE installed, but eclipse is able to compile your java file.
After searching, I got a word "jrew". Someone said that jrew is another kind of binary version of javac and some other files contained in JDK.
And Eclipse uses this tool to compile java file without JDK installed.

Yep it is. There are large number of Java compilers are available. javac is not the only one. javac comes with the JDK bundle.

[Eranga]

I also believe that java can't be compiled without java compiler.
But the truth is that even you can't find javac in your computer, eclipse is still able to compile your java file.

So I think now the problem is that what is the SPECIFIC kind of compiler eclipse is using?

Not only in Java, in any language to compile the source code you need a compiler. It's must.

As I said earlier there should be another compile attached to the Eclipse. But sorry I can't comment on that. Because I'm not an Eclipse user. ;) May someone else can comment on this, or may be there are more information about that this in Eclipse web site.

[killua]

Not only in Java, in any language to compile the source code you need a compiler. It's must.

As I said earlier there should be another compile attached to the Eclipse. But sorry I can't comment on that. Because I'm not an Eclipse user. ;) May someone else can comment on this, or may be there are more information about that this in Eclipse web site.

Hi Eranga,:)
I have find one excellent article about Eclipse Compiler. But I can't post a link here with only 2 replys...I've just send the link to you by private message, Could you post the link in this post for me?
Thx a lot!

ONJava.com -- What's New in Eclipse 3.2 Java Development Tools

[georgemc]

Eclipse is a Java app, hence it needs a JRE to run. But it uses its own internal, incremental compiler - ECJ - rather than javac. You can persuade it to use other compilers, but it's rarely worth the effort

[georgemc]

I also believe that java can't be compiled without java compiler.
But the truth is that even you can't find javac in your computer, eclipse is still able to compile your java file.

So I think now the problem is that what is the SPECIFIC kind of compiler eclipse is using?

ECJ: The Eclipse Compiler for Java. It's true that one needs a compiler to compile Java source code, but it needn't be the Sun reference compiler, javac

[Eranga]

Just search on the Google as java compilers, you can have a list, may be some of them never seen before.