import java.rmi.*;
public interface Calculator extends Remote 
{
 public int addNum(int x,int y) throws RemoteException;
}

import java.rmi.*;
public class CalculatorImpl implements Calculator 
{
	public int addNum(int x,int y) throws RemoteException
	{
	System.out.println("Client request to calculate");
	return (x+y);	
	}
}

import java.rmi.*;
import java.rmi.server.*;
public class CalculatorServer 
{
 public static void main (String args[])
 {
	 try
	 {
		 CalculatorImpl c = new CalculatorImpl();
		 System.out.println("Exporting Calculator...");
		 UnicastRemoteObject.exportObject(c);
		 Naming.bind("rmi://localhost/MyCalculator",c);
		 System.out.println("Register Calculator!");
	 }
	 catch (Exception e)
	 {
		 System.out.println(e);
	 }
 }
}

Exporting Calculator...
java.rmi.StubNotFoundException: Stub class not found: CalculatorImpl_Stub; nested exception is: 
	java.lang.ClassNotFoundException: CalculatorImpl_Stub

echo $JAVA_HOME
/usr/lib/jvm/java-6-sun
echo $CLASSPATH
/usr/lib/jvm/java-6-sun