Hugo van Elk

Your right, I do not think it is fair. At leat, at the time of purchase, they should have announced it. Maybe we should complain?
BTW, does anyone know whether certificates of other companies expire? For instance Sybase or IBM certificates?
/Hugo
SCJP SCJD

I too received my SCJD certificate, today. I find it quite shocking that is expires within two years. Within five years or something, I could live with. But I planed to do the web component exam and the architect exam too. And if they all expire after two years, I will take some effort to keep the four java certificates valid. I am not sure whether I find it worth the effort.
/Hugo.

... BlockingThread's are started, one for each record. The LockManager who tries to lock the database then joins all these threads, and then the LockManager has locked the whole database.
I think it's a nice solution - what do you think?!
[ December 11, 2002: Message edited by: Detlev Beutner ][/QB]
Hi Detlev,
Congratualations, great achievement!
Nice that you describe your solution in detail. But with regard with the total lock, I can think of one drawback: you start up 1 thread for every record in the database. A thread takes several Megabyte RAM initially, and also consumes other system resources like file pointers. So, if the database has enough records, the system will slow down or crash...
/Hugo.

Don't worry, yesterday I uploaded 78 .java files (137 classes). Most of them for the GUI... I think 26 java files is quite moderate

Hi Debra
I would like to thank you for explaining the MVC design. After I redesigned my gui using you ideas, it looks much better!
/Hugo.

Hi Mike
Contratulations, a you did a very good job!
Creative idee to have a connection object. Can you tell something about it? Where there as many instances of the connection object as there are client sessions? And if so, how did the connection objects communicate?
Thanks in advanance.
/Hugo.

Hi Debra
Very kind of you to answer all our questions.
The discussion on MVC is realy an eye opener for me.
For the criteria search, you let the VIEW ask the CONTROLLER to fetch the data from the model. Now I am trying to understand you model, I was wondering whether it could be ok to let VIEW ask MODEL directly to perform the criteria search. This seems ok with the model, going over the 'State query' line.
Is that true, could the VIEW ask the MODEL instead of the controller to perform the search?
/Hugo.

Originally posted by umar hathab:
Hi,

I want to use an object as a hashmap.I dont want any other functionality fo hashmap ...
A.Umar

Hi Umar
If you do not need other functionality, why don't you just instantiate java.util.HashMap? You don't need to subclass or wrap it...

CUU
/Hugo.

Hi Debra
Congratulations, it is the score one dreams of... I never saw a higher score.
I would like to have your advise on two things. Did you implement a thread cleaning up locks of dead clients? And also, did you use a rmi code base? Or did you provide de sub and the interface in the client jar?
Thanks in advance,
/Hugo.

Hi
Maybe using a debuger is a good idee? I used jdb and it helped me out several times.
Greetz,
/Hugo.

A proxy delegates to an instance of the same type as the proxy. A facade not.

Originally posted by Robin Underwood:
The only caching I have is on the client side.

I mean server side to avoid locking overhead an disk access. The serverside cache is not locked for non-destructive methods, for reading there is no locking overhead at all. That would be the benefit. But the assignment does not stress this point.
/Hugo.

Hi!
I am spending some hours designing a cach for our database. But now I am in doubt.
Do we need a cach in our database?
What do you think? I guess not, since it has rarely been a topic in this discussion group.
On the other hand, the assignment says:'Note that the locking required is effectively a "write" lock only'. And it is fun to implement. But overdesigning is not rewarded I suppose.
/Hugo

I guess the format the file is writen to disk cannot be changed. E.g, you cannot choose to stream DataInfo's to file. But the number of records can be changed I suppose.
/Hugo.

Hi Erick
You are right, I observed this behaviour too.
I think from a technical point of view, the best thing would be to check that the record number in the parameter DataInfo has a value between 1 and getRecordCount().
But I want to touch the code as less as possible, so I'm still in a doubt too. Now that we know this behaviour, we can avoid it:
do the validity check youself before invoking modify or delete.

/Hugo.