How to Run a Compiled Component

Question

I am sooo new to JAVA. I bought a book (O'Reilly) to learn Java. I loaded the JAVA complier and the JAVA run time (1.5). I also loaded an IDE called Eclipse. I tried to run some of their example code, but it wouldn't work - this is the error I got "The project was not built since its build path is incomplete. Cannot find the class file for java.lang.Enum. Fix the build path then try building this project     LearningJava               August 11, 2006 4:16:35 PM"
So I tried to use the command line to run basic JAVA. I have a simple program from the book - "HelloJava". I got it to compile with javac command, but when I go to "run" this with the java command, this is the message that I receive
"Exception in thread "main" java.lang.NoClassDefFoundError:" which kind of sounds like I am missing something - same as with Eclipse message above.
I have reloaded everything two times - what can I be doing wrong.
This is supposed to be simple? But I can't even get the sample programs to run. Here is the sample program I did get to compile:
public class HelloJava
public static void main( String[] args ) {
     System.out.println("Hello, Java!");
public class HelloJava
public static void main( String[] args ) {
javax.swing.JFrame frame = new javax.swing.JFrame( "Hello, Java!" );
frame.setSize( 300, 300 );
frame.setVisible( true );
import javax.swing.*;
public class HelloJava
public static void main( String[] args ) {
JFrame frame = new JFrame( "HelloJava" );
     JLabel label = new JLabel("Hello, Java!", JLabel.CENTER );
frame.getContentPane().add( label );
frame.setSize( 300, 300 );
frame.setVisible( true );
import javax.swing.*;
public class HelloJava
public static void main( String[] args ) {
JFrame frame = new JFrame( "HelloJava" );
frame.add( new HelloComponent() );
frame.setSize( 300, 300 );
frame.setVisible( true );
class HelloComponent extends JComponent {
public void paintComponent( java.awt.Graphics g ) {
g.drawString( "Hello, Java!", 125, 95 );
Why can't I get this to execute??? Thank you!!!

Answer 1

remove the CLASSPATH setting which might have been set by
Eclipse or other tools.
on windows platform before compiling and running from the command
prompt give the command
SET CLASSPATH=
to clear any CLASSPATH setting.