resultSet.next() behaviour

[Sherif Shehab]

Hi Guys ,

i got a weird behaviour for resultSet.next() in line 16 .. here is the code :

  
 ResultSet rsMethod = pStat.executeQuery();

if (rsMethod.next() == false) // 1
			{
				sherifutilObj.isNoRecords = true;
				new ReportDisplay().isNoRecords(sherifutilObj.isNoRecords);

				return;

			}

			else
			{
				new ReportDisplay().isNoRecords(sherifutilObj.isNoRecords=false);
				while (rsMethod.next()) // 2   ( the problem is here )
				{
					sherifutilObj.vATMStatus_Seq.add(rsMethod.getString(1));
					sherifutilObj.vATMStatus_date.add(rsMethod.getString(2));
					sherifutilObj.vATMStatus_time.add(rsMethod.getString(3));
					sherifutilObj.vATMStatus_computer.add(rsMethod.getString(4));
					sherifutilObj.vATMStatus_port.add(rsMethod.getString(5));
					sherifutilObj.vATMStatus_user.add(rsMethod.getString(6));
					sherifutilObj.vATMStatus_message.add(rsMethod.getString(7));
					sherifutilObj.vATMStatus_caller.add(rsMethod.getString(8));
					records++;
				}
			}  
sherifutilObj.closeDbConnection(sherifutilObj.rsMethod, sherifutilObj.pStat, sherifutilObj.con); // 3

the problem is when i debug this code it goes to 1 to checks the conditon and this returns false , so it goes to 2 then execute it , then goes directly to 3 without executing what inside while although the conditon in 1 returns false , and i run the query outside the code i found it is returning data , so what i'm missing ??

[David O'Meara]

each call to next moves you forward in the ResultSet, so the while loop will never see the first item because next is always called twice before it gets to that code.
One in the if, one at the start of the 'while'

[Sherif Shehab]

David O'Meara wrote:each call to next moves you forward in the ResultSet, so the while loop will never see the first item because next is always called twice before it gets to that code.
One in the if, one at the start of the 'while'

Thanks David the problem was solved when i commented the if , but i still need to check the resultset before i go to while, how i can do that ?

[Campbell Ritchie]

And never write == false or == true. You can get compiler errors, or worse, logical errors, if you write = by mistake, and == false is poor style.

If you want to check the next method returns false, write

if (!mySR.next()) . . .

[Sherif Shehab]

Campbell Ritchie wrote:And never write == false or == true. You can get compiler errors, or worse, logical errors, if you write = by mistake, and == false is poor style.

If you want to check the next method returns false, write

if (!mySR.next()) . . .

Hi Campbell ,
this (f (!mySR.next()) ) will not work in case there is only one row retrieved ..

[David O'Meara]

from your code it looks like you are only expecting zero or one rows, so the while loop is superfluous

if( rs.next())
{
    //process one row
}
else
{
    /// no results
}

[Sherif Shehab]

David O'Meara wrote:from your code it looks like you are only expecting zero or one rows, so the while loop is superfluous

if( rs.next())
{
    //process one row
}
else
{
    /// no results
}

what do you think i'll use , just in case there are more than 1 row retrieved

int rowCount = rs.getRow ();
if (rowCount > 0)
{
//..while 
}   
else 
{
 // do something else 
}

 

Am i right ?

[David O'Meara]

that depends on whether you expect more than one row.
For more than one row there are several options, but it could look like this:

if(rs.next())
{
    do{
        process(rs);
    }while(rs.next());
}
else
{
    // no results
}

It all depends.

[Sherif Shehab]

Thanks Guys for the advice ..

[Campbell Ritchie]

There is no significant difference in functionality between !boo and boo == false, but !boo is much neater and less error-prone.

If you can set up your booleans so you can always say if (boo) . . . and avoid the ! in if (!boo) . . . that would be even better. But it is sometimes impossible.

[Malhar Me]

 if (rs.next() == false) {
                        
                    } else {
                        rs.previous();
                    }   

rs.next() increase by 1 in if, if the record is their
then it wil execute the else block that time again decrese the count by 1 i.e. it again to its original position.

Hope it will help you...

[Campbell Ritchie]

Sherif Shehab wrote:. . .
Hi Campbell ,
this if (!mySR.next()) ) will not work in case there is only one row retrieved ..

Why not? It ought to.

And sorry I didn't notice your reply earlier.