Re: Determine index from array reference?

From:

Knute Johnson <nospam@rabbitbrush.frazmtn.com>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 24 Jan 2007 18:10:23 -0800

Message-ID:

<ikUth.306680$Pv5.292740@newsfe17.lga>

Patricia Shanahan wrote:

Knute Johnson wrote:

Is there a way to determine the index of an array element given a
reference?

Object[] obj = new Object[8];

Object q = obj[2];

Is it possible to get 2 from q other than iterating through all values
of obj[] and testing for equality of the reference?

Thanks,

This type of question always seems a little backwards to me. I tend to
think the other way round. Not "How do I do this with an array?" but "I
need to do these accesses. What data structure should I use?".

Why an array? What other operations are being done on it?

Patricia

Thanks everybody for your replies. And since Patricia asked the big
question maybe I should give up some more information about what exactly
I'm trying to do.

I asked about an array because that's what I have now. An array of
JTextFields that have ActionListeners attached. In the AL I need to
update another array. So what I had done in the past was to extend
JTextField and add an int variable to hold an index value for the
JTextField. I added a getIndex() method and in my ActionListener I use
that method to acquire the index to modify my other array.

So I could have checked the JTextField reference against all the others
in the array and gotten an index that way but that didn't sound a whole
lot better than the way I was getting it now.

The little program below appears to work with a Vector. What do you
think of that approach?

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;

public class test1 {
     public static void main(String[] args) {
         Vector<JTextField> v = new Vector<JTextField>();
         JTextField test = null;

         for (int i=0; i<10; i++) {
             JTextField tf = new JTextField(" ",10);
             v.add(tf);
             if (i == 3)
                 test = tf;
         }

         System.out.println(v.indexOf(test));
         System.out.println(v.indexOf(null));
     }
}

Anyway, if anybody has a better idea I'm all ears.

Thanks,

--

Knute Johnson
email s/nospam/knute/