[RESOLVED] java noob question

[vb_student]

Hello

i was trng to run a simple "hello world" program, i have got j2sdk1.4.2_04

i am using the windows command prompt

i can get javac to compile to come up with the hello.class file, and my hello world program compiles fine, however when i try to execute it using java hello command i get the following error message

exception in thread "main" java.lang.NoClassDefFoundError: hello

my hello world program contains the following java code

public class hello
{
public static void main ( String[] args )
{
System.out.println("Hello World");
}
}

please can you guys help me

[ComputerJy]

http://www.vbforums.com/showthread.php?t=405111

[vb_student]

hey computerjy i had added ;c:\j2sdk1.4.2_04\bin to my path, the path variable looks like
C:\Program Files\Alias\Maya6.0\bin;%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;C:\Program Files\VoiceAge\Common;c:\matlab6p5\bin\win32;C:\Program Files\Rational\common;C:\Program Files\QuickTime\QTSystem\;c:\j2sdk1.4.2_04\bin

i can get the program to compile using javac but it does not execute

[ComputerJy]

make sure that the file name is "hello.java" (Case sensitive)

[ComputerJy]

1- Goto the "java control panel" in control panel
2- goto the "Java" tab"
3- click on "view" under "Java Application Runtime Settings"
4- make sure both user and system have values set and a vaild path.

if any of them doesn't, then Add one or find it

[vb_student]

thanks for the replies

the file is hell.java it produced hello.class upon compilation.
i then tried to do java hello and it came up with the error

i went to the java control panel and under "Java application runtime settings" the user and system have their values sets and the following paths

for the system the path is c:\program files\java\jre1.5.0_01\bin\javaw.exe (product 1.5.0)


for the user the paths are c:\program files\java\jre1.5.0_01\bin\javaw.exe (product 1.5.0_01) &
c:\program files\java\j2re1.4.2_06\bin\javaw.exe (product 1.4.2_06)

[ComputerJy]

try to remove the 1.4.2 from the user

[vb_student]

i could nto remove 1.4.2 from user, the remove button is greyed out.

i disabled 1.4.2 by unchecking the check btton, but i get the same error message, i disabled 1.5.0 by unchecking the check, but the result was the same

[ComputerJy]

There are no more solutions in my head, so I recommend you use an IDE you can get the links from the other thread I gave you

[vb_student]

thanks for the help

i have downloaded netbeans and will use that to learn java

[ComputerJy]

run java as exe files.
This download is a very wonderful tool for all people who can compile java but can't get it to run properly

[CornedBee]

The problem is most likely the CLASSPATH variable. Search this forum for CLASSPATH and you will find the solution.

[ComputerJy]

The problem is most likely the CLASSPATH variable. Search this forum for CLASSPATH and you will find the solution.

we already tried that
But it didn't work

[CornedBee]

Well, I see nothing in this thread to indicate that vb_student checked the CLASSPATH. Just the PATH.

[vb_student]

my CLASSPATH is C:\Program Files\Java\jre1.5.0_01\lib\ext\QTJava.zip

that does not look good to me, should i change it?

[CornedBee]

Yes. Append ";." to the value.

[ComputerJy]

Yes. Append ";." to the value.

No, that's not it
This is not what the classpath should be set to
it should be: C:\Program Files\Java\jdk1.5.0_01\bin
(with or without the ";") it doesn't make a difference if it's at the end of the line

[CornedBee]

No, it should not. There are no Java .class files in that directory, and that is the only thing CLASSPATH is good for.

[eranga262154]

error message shows that the hello.class file can not be found. so after compiling checkout that hello.class file is there.

java is case sensitive. takecare of it.

set the path correctly to your working folder as well.

[vb_student]

thanks for the replies

i am confised, not sure if i should append

";." to the original classpath i.e.

C:\Program Files\Java\jre1.5.0_01\lib\ext\QTJava.zip

or set the class path to

C:\Program Files\Java\jdk1.5.0_01\bin

and should i reset the path to the working folder too?

[CornedBee]

You should only do what I told you to do, i.e. append ;. to the original classpath.

The /bin thing is confusing CLASSPATH and PATH. Adding the working directory to PATH has exactly no effect in Windows.

[vb_student]

eureka, appending the ;. to the original classpath worked.

what does that do?
why was the original classpath pointing to .zip file?

[CornedBee]

The CLASSPATH tells Java where to look for .class files when trying to load classes that you use. It consists of several paths, separated by semicolons. (Colons in *nix.)
The problem is that it really looks only there. If your classpath is set and doesn't contain the current working directory ".", you can't run classes even if their .class file is in the same directory as you are.

My guess is that you installed some Java program that needs the Java QT bindings, and thus sets the CLASSPATH to the ZIP file containing the classes of the binding. This is an incredibly rude thing for an installer to do, but unfortunately it happens.

[vb_student]

thanks for the reply

is classpath an environment variable which is only used with Java?

i just removed the ;. in the classpath in the control panel, however when i do an echo 5CLASSPATH%, i still get
C:\Program Files\Java\jre1.5.0_01\lib\ext\QTJava.zip;. !
why can't i remove the ;.

[CornedBee]

You need to close and re-open the console to have changes in environment variables take effect. And yes, Java is AFAIK the only thing to care about the CLASSPATH.

[vb_student]

thanks for the reply

why does one need to close the command prompt before the changes take place

did windows have the classpath environment variable before java come onto the scene

[CornedBee]

1) Because that's the way environment variables work. Every application has its own set of vars that cannot be modified from the outside, only the inside. The settings you do in the control panel merely change the defaults with which an app is created, but they cannot change the current set of envvars of the running applications. In addition, every program receives the variables of its creator. The creator of the Java process is the console, so Java receives the outdated variables from the console until you close and recreate that process.

2) No. CLASSPATH was invented by Sun. Since it only has meaning for Java applications (there's no such thing as a classloader in other applications), there was no reason for it to be there.

[vb_student]

thamks for the reply

it makes sense now