Error using "java" command

Question

I've just started trying to learn java and what is really ticking me off is that I can't get my applications to run. I use the "javac" command and it works just fine so I can get applets to work but when I use "java" to run applications I get the error message:
"Exception in thread "main" java.lang.NoClassDefFoundError: "(class name)
I've gone back through and checked my environmental variables and paths but get the same results. I've also tried with two versions of the SDK,
1.2.2 and 1.4.1 and I still get the same results.
Anyone PLEASE help, I need to get farther in learning Java!

Answer 1

My First Java Program (for Windows)
Follow these steps:
1. Download and install the Java 2 SDK
2. Make sure your path and classpath are set correctly
3. Type in your first program
4. Compile your first program
5. Run your first program
6. Read the Java tutorial
1. Download and install the Java 2 SDK
Go to the Java website and download the Java 2 SDK, Standard Edition:
http://java.sun.com/j2se/1.4.1/download.html
NOTE: Make sure you download the SDK (leftmost column) and not just the JRE. The JRE (Java Runtime Environment) only contains the stuff necessary to run Java programs, and not the compiler and other tools you need to develop Java programs.
After downloading, run the installation program to install the Java 2 SDK.
2. Make sure your path and classpath are set correctly
After installing, READ THE INSTALLATION NOTES! Lots of people get in trouble and are asking questions in the forums because they were too lazy to read and follow the installation notes. Especially, after installing the Java 2 SDK you need to add the 'bin' directory of the SDK to your PATH, otherwise you will get an error like "javac is not recognized as an internal or external command" or something similar.
If you've installed the Java 2 SDK in C:\j2sdk1.4.1_03, add C:\j2sdk1.4.1_03\bin to the PATH. How you should do this for different versions of Windows is described in the installation notes: http://java.sun.com/j2se/1.4.1/install-windows.html
If you are using a version of the Java 2 SDK older than 1.4, you need to add the current directory (".") to the CLASSPATH environment variable. CLASSPATH is where Java looks for *.class files (compiled Java classes). Since Java 1.4, Java looks in the current directory automatically if the CLASSPATH isn't set, so you don't need to add "." to the CLASSPATH. Again, the installation notes explain what CLASSPATH is and how you should set it.
3. Type in your first program
Start Notepad and type in your first program:
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello World");
}NOTE: Java is case-sensitive. Be careful to type in the program exactly as shown above. Don't type "Helloworld" or "helloworld" or anything else.
Save the file somewhere in a file called "HelloWorld.java". NOTE: Again, the case must be correct. Even though Windows is case-insensitive for filenames, the case must be correct, because Java is case-sensitive. Also watch out that Notepad doesn't append ".txt" to the filename (so that you end up with a file called "HelloWorld.java.txt"). To make things worse, Windows Explorer hides file extensions by default so you don't even see that the file is actually called "HelloWorld.java.txt" instead of "HelloWorld.java".
4. Compile your first program
Open a command prompt, CD to the directory that contains your source file and type:
javac HelloWorld.java
NOTE: Again, the case must be exactly right.
If all goes well, you'll not get any error messages and a file "HelloWorld.class" is generated.
5. Run your first program
To run your program, type:
java HelloWorld
NOTE: Don't type "HelloWorld.class". You are specifying the class name here, not the filename. Ofcourse, the case is important again.
6. Read the Java tutorial
Go to the Java website and follow The Java Tutorial:
http://java.sun.com/docs/books/tutorial/
The chapter "Your First Cup of Java" also explains in detail how to start with Java.
Jesper