cannot find symbol

please help me out ,
what is going wrong with this code

//MyServer.java
package ju.ch38.server;

import java.rmi.*;

public interface MyServer extends Remote
{
int getDataNum() throws RemoteException;
String getData(int n) throws RemoteException;
}//End of MyServer.java

//MyServerImpl.java
package ju.ch38.server;

import java.rmi.*;

import java.rmi.server.*;

public class MyServerImpl extends UnicastRemoteObject
implements MyServer
{
static String hostname = "ubuntu";
static String data[] = {"Remote","Method","Invocation","Is","Greate"};
public MyServerImpl() throws RemoteException
{
super();
}
public int getDataNum() throws RemoteException
{
return data.length;
}
public String getData(int n) throws RemoteException
{
return data[n%data.length];
}
public static void main(String args[])
{
System.setSecurityManager(new RMISecurityManager());
try
{
MyServerImpl instance = new MyServerImpl();
Naming.rebind("//"+hostname+"/MyServer",instance);
System.out.println("I'm registered! ");

}
catch(Exception ex)
{
System.out.println(ex);
}
}
}//end of MyServerImpl.java

when i compiled got this error.

administrator@ubuntu://home/administrator/workspace/JavaTP/src/ju/ch38/server$ javac MyServer.java
administrator@ubuntu://home/administrator/workspace/JavaTP/src/ju/ch38/server$ javac MyServerImpl.java
MyServerImpl.java:9: cannot find symbol
symbol: class MyServer
implements MyServer
^
1 error

thanks for help.