[ptoomey3]

I am trying to figure out how to use project builder while learning java. What I want to do should be very simple. I create a Java tool project called Hello. Hello.java is as follows:

import java.util.*;
import tools.fruit.*;
public class Hello {

public static void main (String args[]) {
Grape test = new Grape();
System.out.println("Hello World!");
}
}


I defined Grape.java elsewhere (outside the project) ~/javastuff/tools/fruit/Grape.java

The code for Grape.java is as follows:

package tools.fruit;
public class Grape {
public Grape() {
System.out.println ("Hello from Grape");
}

}


I compiled Grape.java into a class file...so I now have ~/javastuff/tools/fruit/Grape.class. I had to add ~/javastuff to my search paths "java classes" within the build settings within project builder before the Hello project would compile. I am fine up till this point...basically this changed my classpath to include ~/javastuff..thus allowing the compiler to find my Grape.class. However, once Hello tries to run I get:

Exception in thread "main" java.lang.NoClassDefFoundError: tools/fruit/Grape
at Hello.main(Hello.java:14)

Now, it seems to me that maybe the classpath I defined above only applied to compiling and not during running....because if I use the terminal and go into the build directory and run:
java -classpath ~/javastuff Hello the program
runs fine...able to load the grape class and executes as I would expect. How do you use simple packages in project builder? I have heard you can drop jar files into /Library/Java/Extensions...but I just want to have a directory full of class files all part of a package and be able to import and use them simply. Help!!!

[Michel Fortin]

I suggest you look at the java executable (in the target tab) and edit launch arguements so that you pass the classpath arguments to java.

[depolitic]

If you are learning Java then Java IDE's are more of a pain then a blessing. You would be better of going with a simple text editor. Or something like JEdit see www.jedit.org or BlueJ.

As IDE's tend to hide's the fundamentals and add's a level of complexity into your learning the beginner does not need.

Just my thoughts.

Best of Luck.

[ptoomey3]

Hey,
I have actually used java enough that I've been through the whole command line and blueJ thing. I am now just wanting to try using project builder instead of vi for a change :-).

Anyway..I have made some progress in debugging the problem. I think it has to do with the fact that Project Builder compiles my Hello project into a jar file. I even tried passing the classpath arguement..still failed. I even went to the command line..manually set my CLASSPATH and then tried running the jar file from the command line..failure. If I dig into the project structure and find the class file and run that from the command line it is fine. So, I am convinced somehting is being lost upon creation of the jar file. I just started looking into this avenue and it makes mention of the manifest file. Do you know if would somehow encode a classpath within that somehow? Thanks again.

[Arkham_c]

That's just how classpath works. The easiest way to do it is to build a jar containing all your classes, then run the jar. You don't want to distribute unrolled class files anyway.

If you decide to go this route, look into ant. It's a really nice XML-based java make system. I use it at work to build all our EJB applications.

[ptoomey3]

Just to wrap up the thread...I finally discovered a solution (don't know if it is the best solution) to my problem. Basically what I found was that it was true that once project builder jars the class files together it does not take into account third party libraries. So, once the jar is run it can no longer find reference to packages that are located in an another directory. I tried moving the directory structure where my external package/classes were located into /Library/Java/Extensions to see if that helps...no use. Finally I bundled my classes in the external package into a jar and put the jar into /Library/Java/Extensions (you can also user ~/Library/Java/Extensions though you have to create that directory yourself). Once I did this project builder built and ran everything with no problem. Lastly..the class-path that exists in the manifest file can only reference relative pathnames ...so placing an absolute pathname to some external classes or jars is of no use. Thanks again.