how to initialize java array size to store database ResultSet data?

Question

I'm new to java but my experience with Matlab and C trained me to ALWAYS pre-allocate memory for an array variable before filling that variable inside a loop (e.g. For loop, While loop, etc).

I find myself retrieving data from a database in Java using ResultSet. A quick search shows there's no way to obtain the number of rows in the ResultSet without stepping through it. Thus the basic question: how to pre-allocate array length of a Java variable intended to store the results of the ResultSet query, without knowing the number of rows in that ResultSet?

What's the conventional wisdom? For example, if the ResultSet contains two columns of data, how to place each column into an separate Java array variable?

UPDATE 1: Some background -- I need to place everything returned by the ResultSet into an object so that I may pass that object to a non-Java (e.g. ActionScript) program that communicates with the Java program via this object's contents.

UPDATE 2: Here's the documentation on the conversion rules from Java to non-Java (e.g. ActionScript). Perhaps http://help.adobe.com/en_US/LiveCycleDataServicesES/3.1/Developing/WSc3ff6d0ea77859461172e0811f00f6eab8-7ffdUpdate.html

The way in java is to get result set into a Collection instance, most preferred being ArrayList. You dont need to know the size before hand, for each row you create an object and add it to the list. — prajeesh kumar
– prajeesh kumar, Commented Mar 6, 2012 at 10:55
Array should be used, when size is known to you. You don't know the size, so use any Collection classes as per your requirement — Chandra Sekhar
– Chandra Sekhar, Commented Mar 6, 2012 at 10:57
Not sure how you are handling your inter-program communication, but you can probably do the same you do with arrays with Lists. Worst case scenario, you transform your List into an array (since the list allows you to see its size). — Marcelo
– Marcelo, Commented Mar 6, 2012 at 11:09

Marcelo · Accepted Answer · 2012-03-06 12:58:47Z

3

Why are you adding it to arrays? You can easily iterate through the ResultSet, transform the results to the appropriate Objects, and add them to an ArrayList... gives you much more flexibility than adding to an array.

But if you really need the number of rows, I think you'll need to run a count query before running your original one.

EDIT: From the documentation you linked, it would seem that if you use a Java ArrayList you'd end up with an ActionScript mx.collections.ArrayCollection object instead of the ActionScript Array object you'd get if you used a Java array. Your choice which one to use, just convert List -> array if you can't change your ActionScript code...:

List<MyObject> myList = new ArrayList<MyObject>();
... populate myList from ResultSet ...
MyObject[] array = myList.toArray(new MyObject[myList.size()]);

edited Mar 6, 2012 at 12:58

answered Mar 6, 2012 at 10:55

Marcelo

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ggkmath Over a year ago

I think this is the right answer, but I need more help to fill it in. I created the following more focused thread to address it: stackoverflow.com/questions/9585764/…

simaremare · Accepted Answer · 2012-03-06 10:59:57Z

0

as what Marcelo said, ArrayList is a better option for this problem, but instead of executing a COUNT query to know how many rows is returned, you can trick it by using:

rs.last(); rs.getRow();

then gat back to the first row after,.

answered Mar 6, 2012 at 10:59

simaremare

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