strange error in eclipse

**stevenpalomino** · 06-18-2011, 06:09 AM

Hey everyone.

I'm trying to write a simple program but I keep getting the following error:

Exception in thread "main" java.lang.NoClassDefFoundError: Main
Caused by: java.lang.ClassNotFoundException: Main
at java.net.URLClassLoader$1.run(URLClassLoader.java: 202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.j ava:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:3 07)
at sun.misc.Launcher$AppClassLoader.loadClass(Launche r.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:2 48)

and here is the code:

class apples{
public static void main(String args[]){
int test=6;

if (test==9){
System.out.println("yes");

}
else{
System.out.println("No");
}
}
}

Thanks in advance!

**masijade** · 06-18-2011, 06:22 AM

Well, your "class" is "apples", not Main, so edit the run configuration to call the proper class.

**stevenpalomino** · 06-18-2011, 07:51 AM

I'm not sure I understand. I just need to change apples to main? why's that? I thought you could make up a name for the class?

**pbrockway2** · 06-18-2011, 08:10 AM

You can call the class anything you like. (Within reason, and it is best to start with a capital letter).

The point masijade was making is that you have to tell Eclipse to run the class you mean it to. And not a class called Main which is what you are doing at the moment.

**stevenpalomino** · 06-18-2011, 03:20 PM

Alright I changed the class to Apples and everything works fine and dandy. Why is it that it can't be called main though?

**JosAH** · 06-18-2011, 03:35 PM

Originally Posted by stevenpalomino

Alright I changed the class to Apples and everything works fine and dandy. Why is it that it can't be called main though?

You can call a class (almost) everything you want but you have to tell Eclipse exactly that name if you want to run it; you called your class 'apples' but you told Eclipse that it had to run a class named 'Main'; that, of course, doesn't make sense and the JVM told you so: it couldn't find a class named 'Main'. Eclipse can do a lot for you but it can't corrrect your mental mistakes you made.

kind regards,

Jos

**stevenpalomino** · 06-21-2011, 05:38 AM

Hello everyone,

Here's another weird error I'm getting. Does this make sense to anyone?
Thanks in advance!

Exception in thread "main" java.io.IOException: No such file or directory
at java.io.UnixFileSystem.createFileExclusively(Nativ e Method)
at java.io.File.createNewFile(File.java:883)
at ContactFileDAO.loadContacts(ContactFileDAO.java:19 )
at Menu.<init>(Menu.java:13)
at ContactBook.main(ContactBook.java:10)

**Junky** · 06-21-2011, 05:41 AM

"No such file or directory"

How is that weird? It makes perfect sense to me.

**stevenpalomino** · 06-21-2011, 05:43 AM

but I don't have a thread named "main"?

**Junky** · 06-21-2011, 05:48 AM

Yes you do. All programs have at least one thread.

"ContactFileDAO.java:19"

This is where your problem is. On that line you are doing something with a file that does not exist or at least not where your Java program is looking for it.

Java Code:

System.out.println(FFFF.getAbsolutePath());

After you change FFFF to the name of your variable add that line to your program above the line causing the error and you will find out where your program is trying to find your file.

**stevenpalomino** · 06-21-2011, 05:50 AM

This is line 19. Doesn't really tell me anything :S
file.createNewFile();

**stevenpalomino** · 06-21-2011, 06:58 AM

Here is the program. Anyone find a problem?
Thanks!

Jasons Address Book.zip

**masijade** · 06-21-2011, 07:22 AM

And what is "file" defined as? What is the path that that File object refers to and does that path exist, and do you have permission to write there? If you look at the stacktrace pointed above you will see the call to that method. Come on, you have got to be able to analyse problems better than this.

**stevenpalomino** · 06-21-2011, 07:28 AM

I'm sorry I'm new to Java. I had a friend send me an example file so that I could study it but I couldn't get it to run. I saw this:

Java Code:

File file = new File(dir + FILE_NAME);
		file.createNewFile();

But I'm not sure what I'm supposed to do with it. Sorry I'm not that great at troubleshooting. I'm new to it. Thanks for your help though!

**masijade** · 06-21-2011, 07:30 AM

And what are "dir" and "FILE_NAME" defined as? And does concating them like this lead to a proper a path? Or is the file separator missing between them? As already suggested use println to print the value of the path.

Edit: P.S. this is what comes of blindly copying code with no understanding of what it does. Example code should be used as nothing more than a nudge in the (hopefully) right direction, it should not be cut-n-pasted.

**stevenpalomino** · 06-21-2011, 05:32 PM

There's also this next snippet of code right after it:

Java Code:

Scanner fileReader = new Scanner(file);
		Contacts contacts = new Contacts();

Should that make it work or do I actually need to replace "dir" and "FILE_NAME" with something?

EDIT* Also, my friend just told me he wrote the code on windows and since I'm on a Mac there might have to be a few changes. What should be different?

**masijade** · 06-21-2011, 05:36 PM

I'm sorry, buht I'm out of here.

**stevenpalomino** · 06-21-2011, 05:38 PM

ok Thanks anyway.

**JosAH** · 06-21-2011, 05:44 PM

Originally Posted by stevenpalomino

Should that make it work or do I actually need to replace "dir" and "FILE_NAME" with something?

EDIT* Also, my friend just told me he wrote the code on windows and since I'm on a Mac there might have to be a few changes. What should be different?

dir+FILE_NAME should result in a sensible (potential) file name. Why not print it just before you attempt to create a file:

Java Code: