User talk:Awesomeness

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Archived Talk 20090502

Okay, I need to make a list of bullets. I have made a bullet class and everything, but I need a special list that will let me access all of the bullets in a while/for loop and be able to add and remove them at any time and never mess up. If I did this in a normal array I could do a for loop and access using an increasing number, but I wouldn't know when to stop. In a while loop, if I used while(bulletsArray[x] != null) and then increment x, after I remove my first bullet that say, hit a wall, it will stop there. I need help!

Thanks,

Awesomeness 14:02, 2 May 2009 (UTC)

I think this will do:

ArrayList<Bullet> bullets = new ArrayList<Bullet>();
for (int i = 0; i < bullets.size(); i++) {
    Bullet bullet = bullets.get(i);
    if (bullet.needRemove()) {
        // I think this will work
        // bullets.remove(i--);
        // but usually I do
        bullets.remove(bullet);
        i--;
    }
}

Here I assume that you use ArrayList to store you bullets and your bullet's classname is Bullet. If you use a plain array to keep the bullets, consider change to ArrayList. It is more flexible. » Nat | Talk » 14:09, 2 May 2009 (UTC)

Oh my gosh! You're right! ArrayList is way more flexible! I looked at the documentation; you don't even have to increment or decrement anything! The function remove() shifts the other elements to the left already! Thanks! Awesomeness 14:14, 2 May 2009 (UTC)

Be sure don't use for-each style (for(Bullet bullet : bullets) or you will get ConcurentModificationException when you remove element (this is per java spec, but I still use the for-each style and didn't get this exception actually). And when you scroll through the array like one I mentioned, be sure you do i--, or you will just skip one element. » Nat | Talk » 14:19, 2 May 2009 (UTC)

Oh, you're right. Awesomeness 14:27, 2 May 2009 (UTC)

One suggestion. Don't use bullets.remove(bullet);, use bullets.remove(i); instead because removing by index is far faster than removing by content. Well, with the size the list is in robocode it probably doesn't matter a ton, but removal of list by content, when you already have the index on hand, seems terribly wasteful to me. --Rednaxela 14:45, 2 May 2009 (UTC)

I changed that myself already. =D lol Awesomeness 14:56, 2 May 2009 (UTC)

I've grown very fond of iterators for Lists, this would be my implementation:

ArrayList<Bullet> bullets = new ArrayList<Bullet>();
Iterator<Bullet> i = bullets.iterator();
while (i.hasNext()) {
    Bullet bullet = i.next();
    if (bullet.needRemove()) {
        i.remove();
    }
}

--Skilgannon 15:00, 2 May 2009 (UTC)

Ahhh... I never knew that iterator has remove method so I always using ArrayLisy.get(i) to prevent ConcurentModificationException. Thanks you very much. » Nat | Talk » 15:06, 2 May 2009 (UTC)

---

How do you find the x and y of a robot you've scanned? I see no ScannedRobotEvent.getX() or getY() method. Awesomeness 15:19, 2 May 2009 (UTC)

Trig Trig Trig...

double absBearing = e.getBearingRadians() + getHeadingRadians();
double x = getX() + Math.sin(absBearing) * e.getDistance();
double y = getY() + Math.cos(absBearing) * e.getDistance();

That's all. » Nat | Talk » 15:21, 2 May 2009 (UTC)

Here's a method I use in my utils class (I first saw it in a PEZ bot):

    public static Point2D.Double project(Point2D.Double sourceLocation, 
        double angle, double length) {
        return new Point2D.Double(sourceLocation.x + Math.sin(angle) * length,
            sourceLocation.y + Math.cos(angle) * length);
    }
    // You'd pass it something like: 
    // myLocation = new Point2D.Double(getX(), getY()); 
    // enemyLocation = MyUtils.project(myLocation, absBearing, e.getDistance());

--Voidious 16:15, 2 May 2009 (UTC)

Lastly, I need a way to "dodge" these simulated bullets and to figure out what angle the oppenent bot would be shooting from if it used linear targeting against me. I don't know how to do either of these. Awesomeness 16:31, 2 May 2009 (UTC)

To dodge, use Anti-Gravity Movement, to assume linear firing, use this code:

angle = Utils.normalRelativeAngle(absBearing +  Math.PI + Math.asin((Math.sin(e.getBearingRadians()) * getVelocity())/(20 - 3 * BULLET_POWER)));

replace BULLET_POWER to which you get from energy drop. This prediction use non-iterative no-wall-stopping linear targeting. » Nat | Talk » 16:35, 2 May 2009 (UTC)

Thanks! This fits exactly what I was planning to do! Awesomeness 16:44, 2 May 2009 (UTC)

However anti-gravity confuses me greatly... Awesomeness 17:11, 2 May 2009 (UTC)