How to do this?

[Rudy Yeung]

While I am working on the RMI, I realize that the methods provided by the remote interface are identical to those provided by the data class. This is actually stated in the assignment specification. Currently, my data client coding has a lot of places calling up various data class methods for direct database access. Is there any way I can efficiently call up the remote methods or direct access methods without placing if-else statements in many different places like the following:

  Data data = new Data("db.db"); // local object
  RemoteRequest rr = new RemoteRequest(); // remote object
  int recordCount = 0;
  // the if-else connection checking happens in a lot of paces
  if (isLocalConnection()) // local connection
    recordCount = data.getRecordCount();
  else // remote connection
    recordCount = rr.getRecordCount();

[Rudy Yeung]

Sorry, I want to elaborate my coding a little bit more:

// the following two lines are in the main
Data data = new Data("db.db"); // local object  
RemoteRequest rr = new RemoteRequest(); // remote object  

// the block like the following appears in many places 
...
// the reference rr and data are passed in in some way
int recordCount = 0;  
// the if-else connection checking happens in a lot of places  if (isLocalConnection()) // local connection    
  recordCount = data.getRecordCount();
else // remote connection    
  recordCount = rr.getRecordCount();

[Vladan Radovanovic]

Hi Rudy,

I believe that Sun has given this scenario(local and network connections) on purpose. You are right saying that putting so many if/else statements is a bit awkward.
I really think that sceneario is a great opportunity to demonstrate polymorphism and that is the way I did it.
Vladan
Where a calculator on the ENIAC is equpped with 18,000 vaccuum
tubes and weighs 30 tons, computers in the future may have only
1,000 vaccuum tubes and perhaps weigh 1 1\2 tons.
-- Popular Mechanics, March 1949

[This message has been edited by Vladan Radovanovic (edited March 09, 2001).]

[Rudy Yeung]

Can you elaborate a bit more or maybe provide a snippet of your explanation?

[Vladan Radovanovic]

Originally posted by Rudy Yeung:
While I am working on the RMI, I realize that the methods provided by the remote interface are identical to those provided by the data class.

Because the Data class and your "RemoteRequest" class in this case have identical methods they can implement the same interface. Let's call that interface "DatabaseInterface". That means that Your client can be of type DatabaseInterface.
You can say

 
DatabaseInterface Client = null;
    if connection equals local 
        Client = new Data();
    if connection equals network
        Client = new RemoteRequest();

Now You can simply call any method throughout with Client.methodName
This way you can disconnect and connect back very easily. I am sure that there is a lot of solutions out there that are applications that stay in only one mode once You start them but this way You can switch between local connection and network one whenever You want and as many times as You want.
Hope this helps.
Vladan

[Rudy Yeung]

Vladan,
Thank you for your help. I learn one more thing in OO design.
Rudy

[Rudy Yeung]

I still have a problem in implementing the DatabaseInterface you mention. Though the data and remote objects have the same methods, the remote methods require throwing RemoteException whereas the data class need not. How do you tackle the throwing exception situation?
Rudy

[Rahul Rathore]

Rudy see the discussion here http://www.javaranch.com/ubb/Forum25/HTML/000418.html

[Rudy Yeung]

Oh, I just get stuck at the same place as you guys did. Thanks for the link anyway.
Rudy

[Rudy Yeung]

Rahul and Vlad,
At the end, my coding needs to throw DatabaseException and Exception, say for the modify() method. Does this also happen to you?
Rudy

[joey phillip]

Rudy ,
I defined methods in remote interface like throwing DatabaseException and RemoteException.
for example ,
public DataInfo[] criteriaFind(String criteria) throws DatabaseException,RemoteException;
So in Client side, i am able to catch DatabaseException in local mode and RemoteEception in network.

any suggestions!
joey

[Rudy Yeung]

Joey,
What about your client side? I mean do you have another database interface for the client side, but then as a whole you do not need to throw a general Exception? For me, I have a database interface throwing Exception (just a general exception), which is extended by both the remote and local database interface. The remote database interface will throw the remote and database exeptions, whereas the local database interface will throw only the database exception.
Rudy

[joey phillip]

Rudy,
I have only one interface which is remote interface. I am using the same interface for both local and network mode. read this forum http://www.javaranch.com/ubb/Forum25/HTML/000445.html
where i explained my design.
why do you need to create theree different interaces. I may be wrong here.Could you please explain.
Thanks
joey

[Alex Pakhomov]

Originally posted by Rudy Yeung:
Joey,
What about your client side? I mean do you have another database interface for the client side, but then as a whole you do not need to throw a general Exception? For me, I have a database interface throwing Exception (just a general exception), which is extended by both the remote and local database interface. The remote database interface will throw the remote and database exeptions, whereas the local database interface will throw only the database exception.
Rudy

I [re]used the RMI server IMPLEMENTATION class to connect to the database in local mode. When something is wrong in
the database the implementation class methods throw the RemoteException anyway. It saves a lot of coding time.
- Alex

[Rudy Yeung]

Joey,
The main reason why I use three interfaces is because I do not want to throw the remote exception in the local connection, but just the exception. There is nothing wrong with your design, and I do not think there is anything wrong with mine either. Can someone provide feedbacks on this?
Rudy

[joey phillip]

Rudy,
Since i have declared the Remote interface methods as throwing both DatabaseException and RemotException , when there is some problem in local mode it will be caught by DatabaseException only and not by RemoteException.
Alex,
I think you are declaring the remote interface methods as throwing Remote Exception only.

joey

[Rudy Yeung]

Joey and Alex,
I understand your point and design. From your point of view, do you think my design of having three interfaces is acceptable?
Rudy

[joey phillip]

Rudy,
I was just looking at your design explanation
http://www.javaranch.com/ubb/Forum25/HTML/000474.html.
I didn't find anything wrong.
Initally i did same like you. Then I had a feeling like i am complicating the design and i modified my design. I switched to this design (keeping one interface) almost two weeks before , and i didn't proceed after that because i want to make sure my design is accepatable or not. So i started reading everyone's design.
Thanks
joey

[This message has been edited by joey phillip (edited March 12, 2001).]

[Rudy Yeung]

Joey,
I finally decide to make programming changes and shrink it down to using one single inteface for both the local and remote data access. I think throwing a general exception is worse than throwing a remote exception in the local connection. Comparing to using three interface, a single interface is simple and comparatively easy to maintain in the long-run.
Rudy

[Lisa Foster]

Hi Rudy I have a question I create my instance in main and pass it to my clients constructor but when I use the instance to call the data classes methods problem is it works once the first time when searching the database, but if I create a new instance every time in my search method it works find how do you implement the Data instance in your client..
Thanks Lisa

[Rudy Yeung]

Lisa,
For my design in the client part, I instantiate the data object in the main method. In the long run, this data object may be used in some other places other than the FBN itself. In view of this, I declare a static reference to hold the data object instead of passing the data object to another object. I have an object that serves as an interface between the GUI and the Database. This object will grab the data object and perform various database activity.
Rudy

[Lisa Foster]

Rudy I believe I will myself create one interface I have been following your discussion and I can relate to this very well.
As for my instance problem I will redesign using an interface to connect between my client and database...
Thanks Lisa