RecordNotFoundException in each method

[Sergey Bylokhov]

Hello Everyone,
I know that this theme was discussed early.

But i still do not understand how to implement this requirement:
My DBMain:

// Locks a record so that it can only be updated or deleted by this client.
// If the specified record is already locked, the current thread gives up
// the CPU and consumes no CPU cycles until the record is unlocked.
    public void lock(int recNo) throws RecordNotFoundException;
// Releases the lock on a record.
    public void unlock(int recNo) throws RecordNotFoundException;

And i have this must option in assignment:

Any methods that throw RecordNotFoundException should do so if a specified record does not exist or is marked as deleted in the database file.

All my methods has throws RecordNotFoundException; How I can throw RecordNotFoundException from the find method?

I was try to implement it but get strange results:
This code fails with RecordNotFoundException:

int recNo = 1;
instance.lock(recNo);
instance.delete(recNo);
instance.unlock(recNo);//RecordNotFoundException

Can I just write in javadoc its not necessary to unlock record after delete because it was unlocked inside delete method?

Got a deadlock here because thread starting wait and there is no way to unlock it:

int recNo = 1;
instance.lock(recNo);
instance.lock(recNo);//Can I just throw IllegalStateException here?

Can I lock one record twice from one client? In java doc i see only "Locks a record so that it can only be updated or deleted by this client."
there is no info about locking.


Thanks for help.

[Roel De Nijs]

Hi Sergey,

How I can throw RecordNotFoundException from the find method?

For example when no record is matching the criteria (instead of returning an empty array or null).

Can I just write in javadoc its not necessary to unlock record after delete because it was unlocked inside delete method?

I used the search engine and someone had a similar question. Take a look here.

Kind regards,
Roel

[Sergey Bylokhov]

What about twice locking the same record by the same client. Can i throw IllegalStateException?

Roel De Nijs wrote:Hi Sergey,

How I can throw RecordNotFoundException from the find method?

For example when no record is matching the criteria (instead of returning an empty array or null).

Can I just write in javadoc its not necessary to unlock record after delete because it was unlocked inside delete method?

I used the search engine and someone had a similar question. Take a look here.

Kind regards,
Roel

Yes i know this approach when you extend sun interface and change only signature in this interface. But SUN try to test it in this way

MyDBMain extends DBMain
class Data implements MyDBMain
DBMain = new Data();
//Here I get a trouble because implementation of Data class slightly different from the DBMain requirement.

Strange requirement=(

[Roel De Nijs]

Hi Sergey,

Yes, you can throw an IllegalStateException when a record is trying to lock the same record. In my solution i simply throw an IllegalStateException if a thread/client is trying to lock a record if it has already locked a record (even if he's trying to lock the same record).

I used also my own interface (extending Sun's interface) and added some methods + changed some method declarations (but it were still legal overrides) and I passed the SCJD exam (so did a whole lot of other ranchers), so I don't think it is a problem if you do it too.

Kind regards,
Roel