Newbie: Run-time error

I entered the first example from Head First Java, compiled and attempted to run via the JVM. But, I am getting an error that has me stumped:

Exception in thread "main" java.lang.NoClassDefFoundError: MyFirstApp

I'm a bit puzzled by this. The code is about as simple as it gets:

public class MyFirstApp
{
public static void main (String[] args)
{
System.out.println("I rule!");
System.out.println("The World");
}
}

I'd appreciate some assistance.

TIA

did you compile the class (running the java compiler using javac or in your IDE) ? is the class file on the classpath ?

because the error message just means that the class you want to run can not be found on the classpath.

the classpath is something like a collection of classes (.class files, but also class files in jar files) and resources (e.g. images you can load without using system specific/absolute file paths). you specify it using the -cp or -classpath option.

e.g.
java -cp .;somedir/classes;somejar.jar MyApp

for simple programs (consisting of just the classes, no libraries that are used) it is usualy enough to change to the directory where the class files reside (root of your package structure).

pascal

Hey Steve ,

Welcome to the world of Java.. :-) Hey Bert , A new Novice Added to our Ranch..

Steve , What you can try to figure out is , Have you set the neccesary things to run your first app.. I mean Have you defined the path for your application ? Path variable is very important. What i would suggest you is this.

1)Add path variable to your environmental variables of your machine , If you dont know where they are , Here's it. Point ur mouse to My Computer -> Right Click -> Properties-> Goto Advanced Tab-> Environmental Variables.

2)Click on New under "User Variables" and give the name of the variable as path and value as the Address of the place where you installed j2sdk. For instance , I have it on my c: , So example can be variable name=path, variable value=c:\j2sdk1.4.0\bin, AFter setting this , Save your program in c:\j2sdk1.4.0\bin and then try to run your app again.. i.e save it as c:\j2sdk1.4.0\bin\MyFirstApp.

Have a great day !
Yogendra.

I had the PATH EnVar set to the BIN directory. I had no problems compiling.

I'm confused with teh class settings. I did the typical install of JDK 1.5. The CLASSPATH is set to as follows:

C:\Program Files\Java\jre1.5.0_06\lib\ext\QTJava.zip;

Since I did not set it, it must have been done at install. I am creating a very simple program. The compile placed the .class file in the same directory as the .java file.

I suspect once I get this resolved I'll be off and running. Something just is clicking for me.

Again, thanks for the help.

After compiling, have you confirmed that you actually have a class file (MyFirstApp.class) in the directory? If it's compiling okay, then your PATH variable should be correct.

When running, make sure that you're in the proper directory. The easiest way to do this is to change directories (using the command cd) to where your files are located. For example...

cd c:\myFiles\java
javac MyFirstApp.java
java MyFirstApp

NOTE: You should not need to change any CLASSPATH settings at this point.
[ April 14, 2006: Message edited by: marc weber ]

The class file is in the same directory as the source code.

Directory of C:\Documents and Settings\xxxxxx\My Documents\My Programming\Java\Tutorials\Head First Java

04/14/2006 06:20 PM <DIR> .
04/14/2006 06:20 PM <DIR> ..
04/14/2006 09:05 PM 448 MyFirstApp.class
04/14/2006 06:20 PM 174 MyFirstApp.java
04/14/2006 05:13 PM 153 MyFirstApp.java.bak
3 File(s) 775 bytes
2 Dir(s) 25,477,156,864 bytes free

I ran the JVM from that directory as follows:

C:>java MyFirstApp
Exception in thread "main" java.lang.NoClassDefFoundError: MyFirstApp
[ April 14, 2006: Message edited by: Steve Davies ]

Originally posted by Steve Davies:
...I ran the JVM from that directory as follows:

C:>java MyFirstApp
Exception in thread "main" java.lang.NoClassDefFoundError: MyFirstApp

When you change to that directory (using the cd command), then your prompt should not be just...

C:\>

At the prompt, type cd followed by the directory path...

C:\>cd C:\Documents and Settings\xxxxxx\My Documents\My Programming\Java\Tutorials\Head First Java

This should change your prompt to...

C:\Documents and Settings\xxxxxx\My Documents\My Programming\Java\Tutorials\Head First Java>

Then try to run...

C:\Documents and Settings\xxxxxx\My Documents\My Programming\Java\Tutorials\Head First Java>java MyFirstApp
[ April 14, 2006: Message edited by: marc weber ]

I'm sorry. I was trying to make it more readable. The prompt can be whatever you wish it to be.

For instance:

prompt $N$G

Will get you:

C>

A prompt of:

C:\Documents and Settings\Steven\My Documents\My Programming\Java\Tutorials\Head First Java>

... is just too much information. When I need the path info, I just type

C> CD

I was in the proper directory.

if you're in the proper directory, try this:

java -cp . MyFirstApp

that tells java to use the current directory as (part of?) the classpath.

this is a short term solution, but it might at least let you get the code to run.

Thanks, Fred. I tried it and received the following:

C>java -cp . MyFirstApp
Exception in thread "main" java.lang.UnsupportedClassVersionError: MyFirstApp (Unsupported major.minor version 49.0)
at java.lang.ClassLoader.defineClass0(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)

Maybe I should have stuck with .Net (Just kidding!)

I appreciate the help. Thanks all.

You have compiled the source with a version 1.5 compiler, and now you are attempting to run the source with some lesser version.

You can verify this with:
javac -J-version (you will see 1.5.x)
java -version (you will see 1.y.z where y < 5)

Found it!!!

Darn Oracle SQL*Net threw in their own version of the JVM. Nice of them. I removed it from the PATH and Oila!!!

Thanks all. I appreciate the overwhelming assistance. You don't get this type of response on MSDN.