problem with int[ ]

[Shannon Sims]

Any suggestions how I can create an int array without initially defining it's size? The problem is that I don't know the size of the int array until after I've looped through a collection, but I need to store the ints (x) while looping through the collection in this int array.

If I initialize it with a bogus size, the int array has 0 values which causing another issue. Therefore I need to put only valid values in this array, no zeros unless it's a valid zero.

Here's some sample code if I'm too vague.

   int[] recordsFound = new int[ classSize ];
   int y = 0;
   for( int x = 0; x < classSize; x++ )
   {
      String[] record = read( x );
      if( record[0].startsWith( criteria[0] )
         && record[1].startsWith( criteria[2] ) )
      {
         recordsFound[y] = x;
      }
   }

Thanks in advance for everyone's help!

[Mark Wuest]

I often make an ArrayList. If I need an actual array for something, I can always get one with toArray()...

What are we doing geeking out on a Saturday night? (I'm escaping from my two boys who have two friends over and debating whether to give them all Benadryl).

Mark

[Shannon Sims]

Hi Mark,
Well unfortunately, I cannot use an ArrayList. Got any other ideas.

Yes, unfortunately I'm geeking out on Saturday only because I've put off working on this project way too long. So I am buckling down and working no matter what day it is.

[Barend Garvelink]

You can't define a variable-size array, java arrays are fixed length. However, using your recordsFound array as temporary storage (initialised to the full length of your collection), you can fill it from position 0 up and keep track of how many array elements are valid. Then all you have to do is copy the valid bit over into a new array.

int[] recordsFound = new int[ classSize ];
int lastValidIndex = -1;
int y = 0;
for( int x = 0; x < classSize; x++ )
{
String[] record = read( x );
if( record[0].startsWith( criteria[0] )
&& record[1].startsWith( criteria[2] ) )
{
recordsFound[ ++lastValidIndex ] = x;
}
}

int[] finalResult;
if (lastvalidIndex > -1) {
finalResult = new int[lastValidIndex + 1];
System.arraycopy(recordsFound, 0, finalResult, 0, finalResult.length);
}
else
{
finalResult = new int[0];
}

(edit) I had to remove the [code../code] block because it ate my boldface highlights.

(edit #2) The forum engine ate my explanation, AND there was a bug in my code snippet. Note that the if (lastValidIndex > -1) condition isn't even necessary (code creates a 0-length array and copies 0 elements into the new array if it's not there), but I wrote it out explicitly for clarity or in case you have to throw an exception or something like that.

Hope this helps
[ July 24, 2005: Message edited by: Barend Garvelink ]

[Mark Wuest]

Well unfortunately, I cannot use an ArrayList. Got any other ideas.

Of course, now we're all curious as to why you can't use an ArrayList... Don't tell us it's a homework assignment! Could you use a Vector? If not, you've gone into a realm where this "Semi-Penitent C++ Convert Who Occasionally Thinks He Could Use Pointer" doesn't have an Elegant Solution:

 
   int[] recordsFoundTemp = new int[ SomeSizeIThinkIsLargeEnough ];
   int y = 0;
   for( int x = 0; x < classSize; x++ )
   {
      String[] record = read( x );
      if( record[0].startsWith( criteria[0] )
         && record[1].startsWith( criteria[2] ) )
      {
         recordsFoundTemp[y++] = x;
      }
   }
   int[] recordsFound = new int[y];
   for (int x = 0; x <= y; x++){
      recordsFound[x] = recordsFoundTemp[x];
   }
 

Mark

[Mark Wuest]

Just a nit: I'm occasionally told things like "If it was a snake, it woulda bit you!", so I probably missed it, but I don't see where you increment y in your original code...

Mark

[Barend Garvelink]

Originally posted by Mark Wuest:

 
//...showing only relevant code
   int[] recordsFound = new int[y];
   for (int x = 0; x <= y; x++){
      recordsFound[x] = recordsFoundTemp[x];
   }
 

Mark

Mark,


Two things:
1) this code will throw an ArrayIndexOutOfBounds exception courtesy of the less-than-or-equal operator you used in the middle section of the for-loop.
2) for every element in the loop, this code will do the "array index within bounds" checking. If you use System.arraycopy(Object,int,Object,int,int) instead, the JVM will perform bounds-checking only once.

[Mark Wuest]

Originally posted by Barend Garvelink:

 
//...showing only relevant code
   int[] recordsFound = new int[y];
   for (int x = 0; x <= y; x++){
      recordsFound[x] = recordsFoundTemp[x];
   }
 

Mark<hr></blockquote>

Mark,


Two things:
1) this code will throw an ArrayIndexOutOfBounds exception courtesy of the less-than-or-equal operator you used in the middle section of the for-loop.
2) for every element in the loop, this code will do the "array index within bounds" checking. If you use System.arraycopy(Object,int,Object,int,int) instead, the JVM will perform bounds-checking only once.[/QB]

1) Yup - that's what I get fer writing from the seat of my pants
2) Yup - ditto, I knew that was in there, but couldn't remember where or what it was called! I think we did their homework assignment for them.

Mark

[Barend Garvelink]

Originally posted by Mark Wuest:
I think we did their homework assignment for them.

Uh-huh .



No arraylists could be J2ME, of course .
[ July 24, 2005: Message edited by: Barend Garvelink ]

[Shannon Sims]

Hi all,
Sorry for the lack of response, however I need a break. When you code M-F, the last thing you want to do is spend the entire weekend coding again.

Actually, I'm working on my SCJD certification. One of the requirements is to implemented a method that returns an int array. Basically, I wanted to ensure that the only options I had were to initialize the array or new the int array with a predefined size. So, I guess with all the feedback I got, I will have to store the int values in some kind of collection and then dump them into an int array. Oh well...

Thank you all for your help!

[Shannon Sims]

Mark,
Ah, it looks like I've forgotten to increment my "y". Thanks for bringing that to my attention. It's been hard working on my project using TextPad.

Thanks!