public interface Calculator 
          extends java.rmi.Remote { 
    public long add(long a, long b) 
        throws java.rmi.RemoteException; 
 
    public long sub(long a, long b) 
        throws java.rmi.RemoteException; 
 
    public long mul(long a, long b) 
        throws java.rmi.RemoteException; 
 
    public long div(long a, long b) 
        throws java.rmi.RemoteException; 
}