Animations and SwingUtilities.invokeLater

Question

I would like to use the method SwingUtilities.invokeLater so that all the Swing components of my program are updated by the event dispatch thread, since it is a good practice.

But if I wrap all the code of the main method in SwingUtilities.invokeLater(new Runnable { public void run() { /* code */ }}); the window freezes (which is normal since my code has an animation loop that takes a few seconds to complete). Where should I put that SwingUtilities.invokeLater method?

Program code (without the SwingUtilities.invokeLater method)

import java.awt.Color;
import java.awt.Dimension;
import java.awt.geom.Rectangle2D;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Test {

  public static void main(String[] args) {
    int width = 854;
    int height = 480;
    String title = "Test";
    BufferedImage bufferedImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
    JFrame frame = new JFrame();
    JPanel panel = new JPanel() {
      protected void paintComponent(Graphics graphics) {
        super.paintComponent(graphics);
        Graphics2D graphics2D = (Graphics2D) graphics;
        graphics2D.drawImage(bufferedImage, 0, 0, null);
      }
    };
    frame.add(panel);
    frame.getContentPane().setPreferredSize(new Dimension(width, height));
    frame.pack();
    frame.setTitle(title);
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
    int size = height/3;
    int x = -size;

    while (x <= width) {
      Graphics2D graphics2D = (Graphics2D) bufferedImage.getGraphics();
      graphics2D.setColor(Color.RED);
      graphics2D.fill(new Rectangle2D.Double(x, 0, size, size));
      graphics2D.setColor(Color.GREEN);
      graphics2D.fill(new Rectangle2D.Double(x, size, size, size));
      graphics2D.setColor(Color.BLUE);
      graphics2D.fill(new Rectangle2D.Double(x, 2 * size, size, size));
      graphics2D.dispose();
      panel.repaint();
      ++x;

      try {
        Thread.sleep(10);
      } catch (InterruptedException exception) {
        exception.printStackTrace();
      }
    }

    frame.dispose();
  }
}

Program screenshot

This is an animation in which the three coloured strips are gradually stretching to the right edge of the window.

Answer 1

Here is that self-contained code (good call on posting that, BTW) updated to use a Timer as suggested by @MadProgrammer. In order to access the x variable, it was moved into the action listener defined for the timer. In order to access the Timer from within the action listener, it was moved to being a class attribute. The latter meant it was easier to move the bulk of the code into a constructor for an instance of the object.

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.Rectangle2D;
import java.awt.image.BufferedImage;
import javax.swing.*;

public class Test {

    Timer timer;

    Test() {
        int width = 854;
        int height = 480;
        String title = "Test";
        BufferedImage bufferedImage = new BufferedImage(
                width, height, BufferedImage.TYPE_INT_RGB);
        JFrame frame = new JFrame();
        JPanel panel = new JPanel() {
            @Override
            protected void paintComponent(Graphics graphics) {
                super.paintComponent(graphics);
                Graphics2D graphics2D = (Graphics2D) graphics;
                // when you have an ImageObserver, may as well use it
                //graphics2D.drawImage(bufferedImage, 0, 0, null);
                graphics2D.drawImage(bufferedImage, 0, 0, this);
            }

            @Override
            public Dimension getPreferredSize() {
                return new Dimension(width,height);
            }
        };
        frame.add(panel);
        frame.pack();
        frame.setTitle(title);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        int size = height / 3;

        ActionListener animationListener = new ActionListener() {

            int x = -size;

            @Override
            public void actionPerformed(ActionEvent e) {
                if (x <= width) {
                    Graphics2D graphics2D = (Graphics2D) bufferedImage.getGraphics();
                    graphics2D.setColor(Color.RED);
                    graphics2D.fill(new Rectangle2D.Double(x, 0, size, size));
                    graphics2D.setColor(Color.GREEN);
                    graphics2D.fill(new Rectangle2D.Double(x, size, size, size));
                    graphics2D.setColor(Color.BLUE);
                    graphics2D.fill(new Rectangle2D.Double(x, 2 * size, size, size));
                    graphics2D.dispose();
                    panel.repaint();
                    ++x;
                } else {
                    timer.stop();
                    frame.dispose();
                }
            }
        };
        timer = new Timer(10, animationListener);
        timer.start();
    }

    public static void main(String[] args) {
        Runnable r = () -> {
            new Test();
        };
        SwingUtilities.invokeLater(r);
    }
}