COMP 310 Fall 2012	Lec33:  Chat App API finalization

IUser.receiveData() return type:  DataPacket

Well-Known Data Types

 
• ITextMessage  -- getName(), getTime(), getMsg()
• IAddCommand -- getID(), getCmd()
• IAddUser -- getUser()
• IRemoveUser -- getUser()
• IOk_XmitStatus -- no methods
• IFail_XmitStatus -- getUser(), getMsg()  -- kow what data is, but could not process it.
• INotSupported_XMitStatus -- getUser(), getMsg()  -- knows what data is but does not want to process it.
• IUnknownData_XmitStatus -- getID(), getUser()  -- want cmd to process it.

Change IChatRoom.getUsers()?

What should the return type of this method be? 

• Iterable<IUser>  -- ? votes  *
• Iterable<String> -- ? votes
• None of the above -- ? vote

Starting up the ChatApp application

Remember that in order to chat, your ChatApp program must be BOTH a RMI client AND a RMI server!

• You only need a single class file server: either class file server port as defined in IRMIUtils is fine.
• You only need to set the RMI properties (hostname, codebase, etc) once.
• IRMIUtiles.startRMI() will start the class file server and set the RMI propertiesfor you.

Things that need to get done (NOT A COMPLETE LIST!):

• Create at least one default chatroom sub-system (encapsulated mini-MVC).
  • Create an IChatRoom object
  • Create an IUser object and stub that is added locally to the IChatRoom object.
• Create an IHost object and stub. 
• Publish the IHost stub to your local Registry.

Adding Yourself to a Chat Room

  What are the steps to add yourself to a chat room?   Do you add yourself (your IUser stub) locally and then send a message to everyone to add you to their chat rooms or vice versa?

Be careful!  What if you are already in the room?

Identifying IUsers

• public UUID getUUID()
• Equality of UUID defines equality of IUsers, independent of name.

Question:   Is the UUID value tied to the instance of the IUser or is it tied to the instance of the ChatApp, i.e. the human operator?    That is, if one's model instantiates more than one instance its own IUser implementation, is that a different user or the same user?     Is this an API issue or not?

Overriding equals() and hashCode() in a proxy class to enable standard equality tests:

	private class ProxyUser implements IUser, Serializable {
				
		/**
		 * The decoree
		 */
		private IUser stub;
		
		// --- Other methods and fields elided -----------

		/**
		 * Overridden equals() method to compare UUID's
		 * @return  Equal if UUID's are equal.  False otherwise.
		 */
		@Override
		public boolean equals(Object other){
			if(other instanceof IUser) { // make sure that other object is an IUser
				try {
					// Equality of IUsers is same as equality of UUID's.
					return stub.getUUID().equals(((IUser)other).getUUID());
				} catch (RemoteException e) {
					// Deal with the exception without throwing a RemoteException.
					System.err.println("ProxyUser.equals(): error getting UUID: "+ e);
					e.printStackTrace();
					// Fall through and return false
				}
			}
			return false;
		}		

		/**
		 * Overridden hashCode() method to create a hashCode from that is hashCode of the UUID since
		 * equality is based on equality of UUID.
		 * @return a hashCode of the UUID.	
		 */
		@Override
		public int hashCode(){
			try {
				// hashCode is shorter than UUID, but Java spec says that if two objects are equal then
				// their hashCodes must also be equal, which will be true here since equals() is based on 
				// UUID equality.  Java does NOT require that unequal entities have unequal hashCodes. 
				return stub.getUUID().hashCode();
			} catch (RemoteException e) {
				// Deal with the exception without throwing a RemoteException.
				System.err.println("ProxyStub.hashCode(): Error calling remote method on IUser stub: "+e);
				e.printStackTrace();
				return super.hashCode();  // return some sort of hashCode
			}
		}
	}

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© 2012 by Stephen Wong