Really annoying RMI-related error

Question

Hi,
I'm attempting to write a Message-Passing system so that two people can play chess against each other remotely. On each player's host computer, a ChessPlayer object keeps track of the current board layout and comes up with the player's next move. A ChessServer object handles all of the communication with the remote opponent; it packages up moves from the local player into messages, and ships them off to the opponent's ChessServer. (It also takes messages from the remote opponent and calls the required methods on the local ChessPlayer.)
I have a ChessMove object interface class and a ChessMove implementation class as follows
~~~~~~~~~~~~~~~~~~~
RMIChessMove.java :
package RMI;
import java.rmi.RemoteException;
// Interface for RMI-based chess move
public interface RMIChessMove {
public int sourceRow() throws RemoteException;
public int sourceCol() throws RemoteException;
public int destRow() throws RemoteException;
public int destCol() throws RemoteException;
public int checkFlag() throws RemoteException;
public void setSourceRow(int sr) throws RemoteException;
public void setSourceCol(int sc) throws RemoteException;
public void setDestRow(int dr) throws RemoteException;
public void setDestCol(int dc) throws RemoteException;
public void setCheckFlag (int cf) throws RemoteException;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
RMIChessMoveImpl.java :
package RMI;
import java.rmi.*;
public class RMIChessMoveImpl implements RMIChessMove extends Remote {
String fromPos;
String toPos;
int sourceRow;
int sourceCol;
int destRow;
int destCol;
int checkFlag;
public RMIChessMoveImpl(int sr, int sc, int dr, int dc, int cf) {
int sourceRow=sr;
int sourceCol=sc;
int destRow=dr;
int destCol=dc;
int checkFlag=cf;
public int sourceRow() throws RemoteException {
return sourceRow;
public int sourceCol() throws RemoteException {
return sourceCol;
public int destRow() throws RemoteException {
return destRow;
public int destCol() throws RemoteException {
return destCol;
public int checkFlag() throws RemoteException {
return checkFlag;
public void setSourceRow(int sr) throws RemoteException {
sourceRow=sr;
public void setSourceCol(int sc) throws RemoteException {
sourceCol=sc;
public void setDestRow(int dr) throws RemoteException {
destRow=dr;
public void setDestCol(int dc) throws RemoteException {
destCol=dc;
public void setCheckFlag (int cf) throws RemoteException {
checkFlag=cf;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The RMIChessMove class compiles without any errors, but the compiler comes up with a weird error when i try to compile RMIChessMoveImpl.java which is as follow:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
RMI/RMIChessMoveImpl.java [5:1] '{' expected
public class RMIChessMoveImpl implements RMIChessMove extends Remote {
^
RMI/RMIChessMoveImpl.java [51:1] '}' expected
^
2 errors
Errors compiling RMIChessMoveImpl.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I've tried switching round the "implements RMIChessMove" and "extends Remote" things but then I get this error message:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
RMI/RMIChessMoveImpl.java [5:1] no interface expected here
public class RMIChessMoveImpl extends Remote implements RMIChessMove {
^
1 error
Errors compiling RMIChessMoveImpl.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I'm convinced this should compile because it's based on O'Reilly's "Java Distributed Computing" textbook.
I'll happily give all my duke dollars to anyone who can solve this problem for me asap.
Cheers.

Answer 1

When I create an RMI application I use the following structure:
MyInterface extends Remote
MyInterfaceImpl extends UnicastRemoteObject implements MyInterface
Your code would then look like this:
public interface RMIChessMove extends Remote {
  // ALL methods should throw RemoteException
public class RMIChessMoveImpl extends UnicastRemoteObject implements RMIChessMove {
// implemented methods from RMIChessMove interface + your setters and manipulators
}If you do not do it like this, your RMI will not work. Note that every implementation of your interface (in this case, ít's RMIChessMoveImpl) should extend UnicastRemoteObject. Then you will have to let the rmic compiler loose on that class to compile the skels and stubs.
Also note that interfaces extend eachother, classes extend eachother, but classes implement interfaces.