// Newtonian particle

import java.lang.Object;
import java.awt.Rectangle;

public class Particle extends Object {
  public double x, y, vx, vy, ax, ay;
  public Rectangle box;
  
  public Particle(Rectangle r, double ix, double iy, double ivx, double ivy, double iax, double iay) {
    x = ix;
    y = iy;
    vx = ivx;
    vy = ivy;
    ax = iax;
    ay = iay;
    box = r;
  }

  // update the particle by dt, do elastic collisions
  public void step(double dt) {
    double newx, newy;

    newx = x + vx * dt;
    if (newx < 0 || newx > box.x + box.width)
      vx = -vx;
    else
      x = newx;

    newy = y + vy * dt;
    if (newy < box.y || newy > (box.y + box.height))
      vy = -vy;
    else
      y = newy;
    
    vx += ax * dt;
    vy += ay * dt;
  }
}