Re: Problem with Timer object

In article <48d7da9b$0$28801$b9f67a60@news.newsdemon.com>,
 Knute Johnson <nospam@rabbitbrush.frazmtn.com> wrote:


[...]

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:

<code>
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");
    this.setDefaultCloseOperation(EXIT_ON_CLOSE);
    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);
    this.pack();
    this.setVisible(true);
    subway.beginOperation();
  }
}

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;
    setPreferredSize(
      new Dimension(MAX * DOOR, DOOR * 162 / 100 + 16));
  }

  public void beginOperation() {
    timer.setInitialDelay(200);
    timer.start();
    timer.setInitialDelay(1000);
  }

  @Override public void paintComponent(Graphics g) {
    super.paintComponent(g);
    int width = getWidth() / MAX;
    int height = getHeight();
    int w2 = width / 2;
    g.setColor(Color.gray);
    g.fillRect(xx, yy, width, height);
    g.setColor(Color.black);
    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) {
      timer.restart();
      control.clearButton(curStop);
      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;
    }
    control.randomButton();
    this.repaint();
  }
}

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));
      tb.addActionListener(this);
      if ((i > 0)) tb.setSelected(rnd.nextBoolean());
      stops.add(tb);
      this.add(tb);
    }
  }

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

  public void clearButton(int i) {
    stops.get(i).setSelected(false);
  }

  public void randomButton() {
    if (rnd.nextGaussian() > 2.0537) // ~2%
      stops.get(rnd.nextInt(MAX)).setSelected(true);
  }

  public void actionPerformed(ActionEvent e) {
    JToggleButton button = (JToggleButton)e.getSource();
    button.setSelected(true);
  }
}
</code>