Re: Problem with Timer object

Knute Johnson <>
Tue, 23 Sep 2008 22:19:24 -0700
John B. Matthews wrote:

In article <48d7da9b$0$28801$>,
 Knute Johnson <> wrote: wrote:

Hi , Sorry for that mess . I use tab and space when I typed the code
into the Google window and at the end it displayed like that . My
problem is how to pause the elevator when it reachs a chosen floor
(picked by pressing one button on the button panel). My idea is to
use another Pause( contains another timer ) class to do this . When
the current floor is the destination floor , I use this code segment

Your code was still not compilable and I don't have the time to play
with it. I still think you should try a different approach rather than
all the timers. Animation can be tricky to get working well. I wrote
you an example of how I think you should approach your problem. Adding
pauses for door opening/closing should be just a matter of adding some
new states to the Direction enum and some more logic code to the run()
method and paint the doors.

Note: I used the European convention for the floors. The first floor
above the ground floor is 1.


OP: I would highlight two, related features of Knute's excellent example
to consider as you update your own code. First, Knute's main() creates
all the GUI components on the EDT, using EventQueue.invokeLater().
Without this, an unfortunate choice for the initial delay in a Timer can
lead to null pointer exceptions that are platform dependent. Second,
notice how Knute's paintComponent() redraws the entire component without
adding any components.

Knute: I was intrigued by your example's implementation of runnable. I
have come to like using javax.swing.Timer, as I can adjust the animation
easily in the same code that handles other aspects of the model. I'd be
grateful for any insights you can offer on one approach versus the
other. As an example, here's a subway simulation driven by a Timer:

import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
import java.util.Random;
import javax.swing.*;

/** @author John B. Matthews */
public class Subway extends JFrame {

  public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
      public void run() {
        new Subway();

  public Subway() {
    this.setTitle("Subway Simulation");
    ButtonPanel control = new ButtonPanel();
    SubwayPanel subway = new SubwayPanel(control);
    this.setLayout(new BorderLayout(0, 8));
    this.add(Box.createVerticalStrut(8), BorderLayout.NORTH);
    this.add(subway, BorderLayout.CENTER);
    this.add(control, BorderLayout.SOUTH);

class SubwayPanel extends JPanel implements ActionListener {
  public static final int MAX = 8; // Max stops
  private static final int DX = 4; // Initial velocity
  private static final int DOOR = 100; // Preferred width
  private int dx = DX;
  private int xx = 0;
  private int yy = 0;
  private Timer timer = new Timer(40, this); // ~25 Hz
  private ButtonPanel control;
  private boolean loading;

  public SubwayPanel(ButtonPanel control) {
    this.control = control;
      new Dimension(MAX * DOOR, DOOR * 162 / 100 + 16));

  public void beginOperation() {

  @Override public void paintComponent(Graphics g) {
    int width = getWidth() / MAX;
    int height = getHeight();
    int w2 = width / 2;
    g.fillRect(xx, yy, width, height);
    g.drawRect(xx, yy, width, height - 1);
    if (loading) g.fillRect(xx + w2 / 2, yy, w2, height);
    else g.drawLine(xx + w2, yy, xx + w2, yy + height);

  // Handle Timer events
  public void actionPerformed(ActionEvent e) {
    int width = getWidth() / MAX;
    int height = getHeight();
    int curStop = Math.min(xx / width, MAX - 1);
    boolean selected = control.getButton(curStop);
    if (Math.abs(xx % width) < DX && selected) {
      loading = true;
    } else {
      xx += dx;
      if (xx < 0) {
        dx = -dx;
        xx = 0;
      if (xx > (MAX - 1) * width) {
        dx = -dx;
        xx = (MAX - 1) * width;
      loading = false;

class ButtonPanel extends JPanel implements ActionListener {
  private static final int MAX = SubwayPanel.MAX;
  private static final Random rnd = new Random();
  private ArrayList<JToggleButton> stops =
    new ArrayList<JToggleButton>();

  public ButtonPanel() {
    this.setLayout(new GridLayout(1, MAX));
    for (int i = 0; i < MAX; i++) {
      JToggleButton tb = new JToggleButton("Stop " + (i + 1));
      if ((i > 0)) tb.setSelected(rnd.nextBoolean());

  public boolean getButton(int i) {
    return stops.get(i).isSelected();

  public void clearButton(int i) {

  public void randomButton() {
    if (rnd.nextGaussian() > 2.0537) // ~2%

  public void actionPerformed(ActionEvent e) {
    JToggleButton button = (JToggleButton)e.getSource();

For the elevator example the Runnable was the simplest way to implement
the animation and to be able extend it.

I've been on a forever quest for more speed and smoothness in animation.
  java.util.Timer is not very consistent in its intervals.
javax.swing.Timer is a little better but if you are doing much on the
EDT that doesn't hold true either. And it has a larger practical
minimum interval than java.util.Timer. Thread.sleep() is probably the
best of those three although it can still vary considerably too. For
some things I've been doing lately that require exceptional smoothness
I've been using a loop and System.nanoTime(). I've been playing with a
very small sleep, 1ms or so, in the loop but it is smoother without it.
  This uses a lot of processor and will only really work on
multi-processor machines but it is the smoothest I've found so far.

The other issue in animation performance is draw time. The newer
compilers are much faster but direct rendering using a BufferStrategy on
a Panel or Window/JWindow, under Windows XP anyway, is very very fast.
All of my work animation has been on Windows machines and I know that it
is a completely different game under Linux. And really most of what
I've been doing isn't animation like a movie, but has been scrolling
text or images.

We are doing a project in Las Vegas in a new casino that has three huge
rear projection screens in their Race and Sports Book. On the bottom
they have a scrolling window like the ticker windows on CNN or some of
the news stations. I have spent a huge amount of time getting that to
be smooth. Turns out your eye is very sensitive to jerky motion in a
horizontal direction, much more so than vertical. My biggest concern
now is computer life running the processors at 90% 24/7. I'm afraid
that the heat will shorten their life but I guess I won't know until it
breaks :-).

So for most things, the java.util.Timer will be perfect. Sometimes the
implementation is slightly simpler with a runnable loop as was the
elevator case.


Knute Johnson
email s/nospam/knute2008/

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