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Groups > comp.lang.java.programmer > #9526

Re: iteration blues

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On Nov 4, 2:34 am, Robert Klemme <shortcut...@googlemail.com> wrote:
> On 11/03/2011 04:37 PM, bob wrote:
>
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> > So, I wrote this code for some particle effects:
>
> > package com.coolfone.particles;
>
> > import java.util.Iterator;
> > import java.util.Vector;
>
> > import javax.microedition.khronos.opengles.GL10;
>
> > public class FireManager {
> >    static Vector<Particle>  particles = new Vector<Particle>();
>
> >    public static void startfire(float x, float y) {
> >            for (int ctr = 0; ctr<  100; ctr++) {
> >                    Particle p = new Particle();
> >                    p.x = (float) (x + Math.random()-.5);
> >                    p.y = (float) (y + Math.random()-.5);
> >                    p.dx = (float) (Math.random()-.5)/4f;
> >                    p.dy = (float) (Math.random()-.5)/4f;
> >                    p.timeleft = (int) (Math.random() * 50 + 50);
> >                    particles.add(p);
> >            }
> >    }
>
> >    public static void burnfire() {
> >            Iterator<Particle>  i = particles.iterator();
> >            Vector<Particle>  removelist = new Vector<Particle>();
> >            while (i.hasNext()) {
> >                    Particle p = i.next();
> >                    p.move();
> >                    p.timeleft--;
> >                    if (p.timeleft == 0) removelist.add(p);
>
> >            }
> >            particles.removeAll(removelist);
>
> >    }
>
> >    public static void drawfire(GL10 gl) {
> >            Iterator<Particle>  i = particles.iterator();
> >            while (i.hasNext()) {
> >                    Particle p = i.next();
> >                    p.draw(gl);
> >            }
> >    }
>
> > }
>
> > I'm concerned about inefficiency in the burnfire function.  Does
> > anyone know how to rewrite this quickly if particles was a linked
> > list?  The main issue is that I'm not sure if removing items during
> > iteration messes up the iterator.
>
> I'm surprised nobody seems to mention Iterator.remove().
>
> public static void burnfire() {
>    for (final Iterator<Particle> i = particles.iterator(); i.hasNext();) {
>      final Particle p = i.next();
>      p.move();
>      p.timeleft--;  // Direct access to member, bad!
>
>      if (p.timeleft == 0) {
>        iter.remove();
>      }
>    }
>
> }
>
> This can be used regardless of container type.  Efficiency depends on
> the ratio of removed elements.  If you remove much and do not need
> indexed access (i.e. via List.get(int)) you can use a LinkedList.
> Otherwise use ArrayList as indicated already.  There is no point in
> using Vector these days any more.
>
> And btw, do not be concerned about performance, measure it.  Results may
> be surprising.
>
> Kind regards
>
>         robert

Just what I needed.  Thanks.

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iteration blues bob <bob@coolgroups.com> - 2011-11-03 08:37 -0700
  Re: iteration blues Knute Johnson <nospam@knutejohnson.com> - 2011-11-03 08:51 -0700
    Re: iteration blues Lew <lewbloch@gmail.com> - 2011-11-03 09:32 -0700
      Re: iteration blues Arne Vajhøj <arne@vajhoej.dk> - 2011-11-04 21:00 -0400
        Re: iteration blues spk <jhic@speak.invalid> - 2011-11-05 07:48 -0400
  Re: iteration blues Henk van Voorthuijsen <voorth@xs4all.nl> - 2011-11-03 09:31 -0700
    Re: iteration blues Lew <lewbloch@gmail.com> - 2011-11-03 13:50 -0700
      Re: iteration blues Henk van Voorthuijsen <voorth@xs4all.nl> - 2011-11-04 08:07 -0700
    Re: iteration blues Arne Vajhøj <arne@vajhoej.dk> - 2011-11-04 21:02 -0400
  Re: iteration blues Roedy Green <see_website@mindprod.com.invalid> - 2011-11-03 10:08 -0700
  Re: iteration blues Travers Naran <tnaran@gmail.com> - 2011-11-03 22:22 -0700
  Re: iteration blues Robert Klemme <shortcutter@googlemail.com> - 2011-11-04 10:34 +0100
    Re: iteration blues Lew <lewbloch@gmail.com> - 2011-11-04 10:46 -0700
      Re: iteration blues Robert Klemme <shortcutter@googlemail.com> - 2011-11-04 23:55 +0100
        Re: iteration blues Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-04 21:06 -0400
        Re: iteration blues Lew <lewbloch@gmail.com> - 2011-11-04 20:30 -0700
        Re: iteration blues bob <bob@coolgroups.com> - 2011-11-05 12:40 -0700
          Re: iteration blues Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-11-05 16:14 -0400
            Re: iteration blues Lew <lewbloch@gmail.com> - 2011-11-05 13:41 -0700
    Re: iteration blues bob <bob@coolgroups.com> - 2011-11-04 13:42 -0700

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