Moving a ball around

Question

I have a really annoying problem that I can't figure out.. I think it's a problem with my casting.
      float delta = System.currentTimeMillis() - timeAtLastTick;
      timeAtLastTick = System.currentTimeMillis();
      float ychange = (float)(ball.getYVol()*(delta/1000));
      float xchange = (float)(ball.getXVol()*(delta/1000));
      float newx = xchange + ball.getXPos();
      float newy = ychange + ball.getYPos();
      System.out.println("xchange: " + xchange + " newx: " + newx + " oldx: " + ball.getXPos());
      ball.setYPos(newy);
      ball.setXPos(newx);I call that code every time I go through my game loop. xchange and ychange are always possitive, but newx and newy are always equal to oldx and oldy! Any thoughts?

Answer 1

Nope, I copied and pasted that code. The only difference is that it was wrapped up in a method. Here's my tick() method:
public void tick()
      float delta = System.currentTimeMillis() - timeAtLastTick;
      timeAtLastTick = System.currentTimeMillis();
      float ychange = (float)(ball.getYVol()*(delta/1000));
      float xchange = (float)(ball.getXVol()*(delta/1000));
      float newx = (xchange + ball.getXPos());
      float newy = (ychange + ball.getYPos());
      ball.setYPos(newy);
      ball.setXPos(newx);
      System.out.println("xchange: " + xchange + " newx: " + newx + " oldx: " + ball.getXPos());
}What's being printed looks something like this:
xchange: 7.5 newx: 5.48133175E11 oldx: 5.48133175E11
xchange: 16.0 newx: 5.48133175E11 oldx: 5.48133175E11
xchange: 7.5 newx: 5.48133175E11 oldx: 5.48133175E11
xchange: 8.0 newx: 5.48133175E11 oldx: 5.48133175E11
...Every time I go through my gameLoop, I call tick, and then I call repaint on the panel that's drawing my ball. Here's the drawing code:
      g2.fillOval(Math.round(ball.getXPos()), Math.round(ball.getYPos()), BALL_WIDTH, BALL_HEIGHT);It definately wasn't a problem with using the wrong class files, but I deleted them all and recompiled anyway. That didn't work....
Here's my Ball.java code if anybody wants to look at it:
package com.cyntaks.gaming.arcade.pong;
public class Ball
  private float xPos;
  private float yPos;
  private double xVol;
  private double yVol;
  public Ball(float xPos, float yPos, float xVol, float yVol)
    this.xPos = xPos;
    this.yPos = yPos;
    this.xVol = xVol;
    this.yVol = yVol;
  public float getXPos()
    return xPos;
  public void setXPos(float newXPos)
    xPos = newXPos;
  public float getYPos()
    return yPos;
  public void setYPos(float newYPos)
    yPos = newYPos;
  public double getXVol()
    return xVol;
  public void setXVol(double newXVol)
    xVol = newXVol;
  public double getYVol()
    return yVol;
  public void setYVol(double newYVol)
    yVol = newYVol;
}Well I'm stumped. I'm going to rewrite all of my ball moving/handling/drawing code tomorrow if I don't think of something in my sleep :P
The game is a multiplayer pong game. I had everything working, but then I realized that because the game speed was locked to the refresh rate, the two players' games would become out of sync if their frame rates weren't synced. That's why I implemented this "delta tick" idea. Here's a screenshot of the game in action before I started this delta thing:
http://gaming.cyntaks.com/projects/projects/tempscreens/RLKPong.gif