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

OK, I've just got javac working, some sdk stuff, and now I would like java to do the same. I've compiled a small program:

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

I have compiled it and renamed the hello.class file for just hello as I saw somewhere on google.
Then when I try to run the program:

[thomas@thomas Java]$ java hello
Exception in thread "main" java.lang.NoClassDefFoundError: hello

and nothing else happens. What does it mean?

Hi there Lobais!!!

Well, first, you should not rename the file to hello.class. Class is a "compiled" file created by javac. So, write the code as you did, save it as hello.java then use:

javac hello.java

to compile it. java.class will be created. Use:

java hello

to run the application. A side note on your code too. Java can be really peek about System.out line. Substitute you line for this:

System.out.println("Hello world");

That should work. If it fails, reinstall Java2 SDK, it can install wrongly quite often actually

Good luck!

Well I actually started just with java hello.class, but someone on google wrote that you should remove the .class stuff.

[thomas@thomas Java]$ javac hello.java
[thomas@thomas Java]$ java hello.class
Exception in thread "main" java.lang.NoClassDefFoundError: hello/class
[thomas@thomas Java]$

I installed Java as the wrote on http://www.fedorafaq.org/custom_java.html just with the sdk package. I think I have installed it more than twice already.

yup, the error is here then:

java hello.class

After you've used "javac hello.java" to compile the application, hello.class will be created. However, to run the application, you've to type "java hello" without the extension (.class)

That was the thing i didn't understood. Thank you so much.
But why doesn't this work for Anjuta ?

EXECUTING:
java /home/thomas/Java/hello
----------------------------------------------
Exception in thread "main" java.lang.NoClassDefFoundError: /home/thomas/Java/hello
 
----------------------------------------------
Program exited successfully with errcode (1)
Press the Enter key to close this terminal ...

Hey cool . Well, I've never tried anjuta myself, but everybody says it's great . Sorry that I cannot help ya out with that . However, since we are talking about IDE's, I'd like to recommend DrJava:

http://drjava.sourceforge.net/

It's pretty nice, written in Java, open-source and great for learning Java

Cheers!

OK, I'll have a look on drjava, but it's a little pretty that I doesn't have OS look
Thanks.

Try 'java -classpath . Hello'

Instead of the Anjuta "java $(current.full.filename)" execute command?

If you want to use anjuta you will have to do something slightly different.
For 'java -classpath . Hello', make sure you're in the directory that the file's in (w/ cd).
For anjuta, you'd do something like:
java -classpath $(name.of.anjutas.variable.for.the.files.dir) $(current.full.filename)

I can run the program in the terminal with:

[thomas@thomas Java]$ javac hello.java
[thomas@thomas Java]$ ls
hello.class  hello.java
[thomas@thomas Java]$ java hello
Hello world
[thomas@thomas Java]$

So no need for classpath there.

In Anjuta, what is the variable.for.the.files.dir thing?

I made it. I just changed the java "$(current.full.filename)" for java "$(current.file.name)".
But say me one thing. Why can't linux run the class files without using a program? Whit compiled c files, it just runs them.

Java .class files are not executables. They are the code you wrote in a sort of compressed form (it can be easily decompiled, unlike c code). The java program is needed to run them.

How do I make them into binary?

You "can't", yet. Gcc has an extension that translate java byte code into native code, called gcj. The draw back is, that project is in early stages of development and don't support any graphical interface of java, as Swing.

Also, translating your code into machine language completely kills the purpose of Java, which is portability.

No language is safe, not c/c++ either. There're decompilers for everything. The process of decompiling is known as Reverse Engineering. Take a look here for some decompilers:

http://www.free2space.com/tools/decompilers/setup.html

That said, the two very best ways of protecting your code is: copy right it or release as GPL.

If I was you, I'd more worried to learn Java efficiently (or any other language for that matter) then someone, somehow, in the future, will hack your application. If it does, just sue their pants off. It's quite funny and I bet, profitable