[JAVA] NoClassDefFoundError

[bstefano79]

import java.util.*;
import java.io.*;
import jxl.*;


public class prova
{
	static String foglio = "Foglio1";
      static String filename = "Cadmo.xls";
	static Vector vettore=new Vector();

	public static void main(String[] args) 
	{
		System.out.println("Ciao");
	}

	public prova()
	{
	}
	
	public void f()
	{
		try
		{
			jxl.Workbook w=jxl.Workbook.getWorkbook(new File("Cadmo.xls"));
		}
		catch (Exception e)
		{
			e.printStackTrace();
			//System.out.println(); 
		}
		

	}
}

compilazione> javac -classpath jxl.jar prova.java
NESSUN ERRORE

esecuzione> java prova
ERRORE Exception in thread "main" java.lang.NoClassDefFoundError: jxl/Workbook

perchhhhhhhhhhhhhhhhéééééééééééééé??????