readRecord vs findByCriteria

[Ed Green]

Hello all,
I'm doing B&S assignment, and have the following interface:

 
// Reads a record from the file. Returns an array where each
// element is a record value.
public String [] readRecord(long recNo)

and

 // Returns an array of record numbers that match the specified
// criteria. Field n in the database file is described by
// criteria[n]. A null value in criteria[n] matches any field
// value. A non-null  value in criteria[n] matches any field
// value that begins with criteria[n]. (For example, "Fred"
// matches "Fred" or "Freddy".)
public long[] findByCriteria(String[] criteria);
 

Maybe i'm missing something, but findByCriteria() returns a list of record numbers, which i can't return to the client, so i guess i'll have to do a readRecord() of all the records using that long[], but i've just physically read all of them to do the findByCriteria()!
Seems like a waste. What am i missing?

[Hanna Habashy]

hi Ed:

public String [] readRecord(long recNo)

The readRecord(long recNo) method will come handy if a client knows which record to display. I use this method in delete and update. If a client attempt to delete record n, the client can display record n before deleting it, this way it ensures no records will be deleted by mistake.

[Anthony Watson]

You could call readRecord in findByCriteria to get a record's data to compare to the criteria array.

[Ed Green]

Hi Hanna,
Tnx for the usage ideas, makes sense.

Anthony,
Thanx for the reply, i was thinking the same thing, but i don't know the exact record count, but i guess i could call read with an ever increasing number until i get EOF..

[Hans Nemarich]

ED, you can try something like this to know how many records are:

long dataSection = data.length() - dataLocation;
long len = recSize + DELETED_FLAG_SIZE;
int recTotal = (int) (dataSection / len);