class Step extends TimerTask
{ @Override
  public void run()
  { if (b)
    { x = x_0 + v0x*t;
      y = y_0 + v0y*t + g*t*t/2;
      c=(4*((x-x_1)*(x-x_1)+(y-y_1)*(y-y_1))<(d0+d1)*(d0+d1));
      jPanel1.repaint();
      t+=dt;
      b = (x<w) && (y<h) && (!c);
      if (c) { timer.cancel();} 
    }
    else   { timer.cancel();} 
  }
}