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From: Knute Johnson <nospam@knutejohnson.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: iteration blues
Date: Thu, 03 Nov 2011 08:51:18 -0700
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On 11/3/2011 8:37 AM, bob wrote:
> 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.

while (i.hasNext()) {
 > 			Particle p = i.next();
 > 			p.move();
 > 			p.timeleft--;

             while (--p.timeleft >= 0)
                 p.remove();

 > 			if (p.timeleft == 0) removelist.add(p);


I have a game at http://rabbitbrush.frazmtn.com/asteroids.html that 
demonstrates this code.  I think it is plenty quick for the type of 
animation that is being done.  See the source code on the link at the 
bottom of the page.

-- 

Knute Johnson