关于用循环构造的东西的Java mutator方法

Question

So I have a class that I constructed with a loop. In the constructor I have two while loops which make "grid" of circles. It's supposed to be a scarf for class but I'm calling it chainmail because that sounds cooler. Anyways we're supposed to be able to change the color of the scarf with a different (client) class. I obviously need to add a mutator method to change the color. Luckily there is a mutator for this in objectdraw called setColor(). It works just fine, except when I try to add it to this class it only changes the last circle in the grid. I know why this happens, but I don't know how to fix it. I've commented out the "typical" mutator we've been using in class.

EDIT: Sorry for the confusion guys... this is just the class, I have a client that calls a new ChainMail() and then does a .setColor() on it but it only changes the last framedoval instead of all of them. That's the problem

import objectdraw.*;
import java.awt.*;

public class ChainMail {

  private FramedOval link;

  public ChainMail(int rows,int links,
                   Location p,Color rgb,
                   DrawingCanvas c) {

    double numRows = 0;

    // create the number of rows specified
    while (numRows < rows) {

      double numLinks = 0;

      // create the number of links specified
      while (numLinks < links) {
        link = new FramedOval(p,12,12,c);
        link.setColor(rgb);

        // update the position
        p.translate(8,0);
        numLinks++;
      }

      // move position back to front col and down one row
      p.translate(-8*links,8);
      numRows++;

    }

  }

  public ChainMail(int rows,int links,Location p,DrawingCanvas c) {
    this(rows,links,p,Color.BLACK,c);
  }

  /* this doesn't work, only changes last circle
   * public void setColor(Color c) {
   *   link.setColor(c);
   * }
   */

}

Answer 1

If you move it to class (as shown in commented code) then from where do you call this function ? I think this is what making the difference. Suppose you are doing following :

1. remove "link.setColor(rgb);" from inside the while loop
2. Uncomment public void setColor(Color c) function
3. Create instance of ChainMail (say myChainMail)
4. Call myChainMail.setColor(c)

This scenario will give the result which you have reported ie only last circled gets colored. There are 2 ways to solve the issue :

1. First is what you are already doing
2. Instead of "private FramedOval link;" create "private ArrayList linkList = new ArrayList; Now before while create link variable of type FramedOval. Then after you do link = new FramedOval(p,12,12,c); in while loop add this to above created ArrayList. Now in setColor method of your class iterate over all the items in arraylist and set color on those items

Answer 2

I say you're throwing them away because you do this:

  while (numLinks < links) {
    link = new FramedOval(p,12,12,c);
    link.setColor(rgb);

    // update the position
    p.translate(8,0);
    numLinks++;
  }

But where do you do anything with the FramedOval that you've created? Every time you create a new FramedOval object and have link refer to it, the previous reference gets lost and is likely garbage collected; it's discarded, which doesn't make sense.

Usually you'd do something like:

  List<FramedOval> framedOvalList = new LinkedList<FramedOval>(); // or ArrayList
  while (numLinks < links) {
    link = new FramedOval(p,12,12,c);
    link.setColor(rgb);

    // *** here add the created object to some collection
    framedOvalList.add(link);

    // update the position
    p.translate(8,0);
    numLinks++;
  }

But I don't see you doing anything of the kind.