Java Swing Timer and Animation: how to put it together

1. Don't call updateUI, unless you're dealing with installing a look and feel, it's not doing what you think it is (and it's very inefficient)
2. Don't rebuild the UI each time, this is time consuming work, which is going to make the animation look stilled and staggered and probably flash a lot. Instead, simply update the icon property of the label
3. Use a single Timer, allow it to increment a counter, so you know how many times it's been called and update the die roll and counter on each tick.

Think of the Timer as a kind of loop, where on each iteration (tick), you need to do something (like increment the counter)

(Note- When it looks like the die has "stalled", it's because the image is been displayed more then once in sequence. You could over come this by placing all the images into a List and using Collections.shuffle. Do this three times, adding the result to another List should give you 24, no-repeating sequence (ok, it "might" repeat on the boundaries, but it's better then using Math.random ;))

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private BufferedImage[] dice = new BufferedImage[6];
        private JLabel die;

        public TestPane() {
            try {
                BufferedImage img = ImageIO.read(new File("/Users/swhitehead/Documents/Die.png"));
                int width = 377 / 6;
                for (int index = 0; index < 6; index++) {
                    dice[index] = img.getSubimage(width * index, 0, width, width);
                }
            } catch (IOException ex) {
                ex.printStackTrace();
            }
            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridwidth = GridBagConstraints.REMAINDER;
            die = new JLabel(new ImageIcon(dice[0]));
            add(die, gbc);

            JButton roll = new JButton("Roll");
            add(roll, gbc);

            roll.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    roll.setEnabled(false);
                    Timer timer = new Timer(250, new ActionListener() {
                        private int counter;
                        private int lastRoll;
                        @Override
                        public void actionPerformed(ActionEvent e) {
                            if (counter < 20) {
                                counter++;
                                lastRoll = (int)(Math.random() * 6);
                                System.out.println(counter + "/" + lastRoll);
                                die.setIcon(new ImageIcon(dice[lastRoll]));
                            } else {
                                lastDieRollWas(lastRoll);
                                ((Timer)e.getSource()).stop();
                                roll.setEnabled(true);
                            }
                        }
                    });
                    timer.start();
                }
            });
        }

        protected void lastDieRollWas(int roll) {
            System.out.println("You rolled " + (roll + 1));
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

    }

}