How to save a method that runs continuously in the background until the program ends?

Question

I want to know how to save a method in the background. i.e. this method starts when the program starts and continues to execute its instructions until the program is closed. E.g. let's say I have a "gravity ()" method that continuously decreases a certain value while the program is running. Right now, to try this, using the following program in which im is trying to pull the duke down (gravity) when no keys are pressed. but this does not happen.

import java.awt.*; import java.awt.event.*; import java.awt.image.BufferedImage; import java.io.IOException; import java.net.*; import java.util.HashMap; import java.util.Map; import javax.imageio.ImageIO; import javax.swing.*; public class MoveIcon extends JPanel { private static final long serialVersionUID = 1L; private static final String IMAGE_PATH = "http://duke.kenai.com/misc/Bullfight.jpg"; private static final String IMAGE_PATH_PLAYER = "http://duke.kenai.com/iconSized/duke4.gif"; public static final int STEP = 3; private static final int TIMER_DELAY = STEP * 8; private BufferedImage bkgrndImage = null; private BufferedImage playerImage = null; private Map<Direction, Boolean> directionMap = new HashMap<Direction, Boolean>(); private int playerX = 0; private int playerY = 0; enum Direction { UP(KeyEvent.VK_UP, 0, -1), DOWN(KeyEvent.VK_DOWN, 0, 1), LEFT(KeyEvent.VK_LEFT, -1, 0), RIGHT(KeyEvent.VK_RIGHT, 1, 0); private int keyCode; private int xDirection; private int yDirection; private Direction(int keyCode, int xDirection, int yDirection) { this.keyCode = keyCode; this.xDirection = xDirection; this.yDirection = yDirection; } public int getKeyCode() { return keyCode; } public int getXDirection() { return xDirection; } public int getYDirection() { return yDirection; } } public MoveIcon() { try { URL bkgrdImageURL = new URL(IMAGE_PATH); URL playerImageURL = new URL(IMAGE_PATH_PLAYER); bkgrndImage = ImageIO.read(bkgrdImageURL); playerImage = ImageIO.read(playerImageURL); setPreferredSize(new Dimension(bkgrndImage.getWidth(), bkgrndImage.getHeight())); } catch (MalformedURLException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } for (Direction direction : Direction.values()) { directionMap.put(direction, false); } setKeyBindings(); Timer timer = new Timer(TIMER_DELAY, new TimerListener()); timer.start(); } private void setKeyBindings() { InputMap inMap = getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW); ActionMap actMap = getActionMap(); for (final Direction direction : Direction.values()) { KeyStroke pressed = KeyStroke.getKeyStroke(direction.getKeyCode(), 0, false); KeyStroke released = KeyStroke.getKeyStroke(direction.getKeyCode(), 0, true); inMap.put(pressed, direction.toString() + "pressed"); inMap.put(released, direction.toString() + "released"); actMap.put(direction.toString() + "pressed", new AbstractAction() { private static final long serialVersionUID = 1L; @Override public void actionPerformed(ActionEvent e) { directionMap.put(direction, true); } }); actMap.put(direction.toString() + "released", new AbstractAction() { private static final long serialVersionUID = 1L; @Override public void actionPerformed(ActionEvent e) { directionMap.put(direction, false); } }); } } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); if (bkgrndImage != null) { g.drawImage(bkgrndImage, 0, 0, null); } if (playerImage != null) { g.drawImage(playerImage, playerX, playerY, null); } } private class TimerListener implements ActionListener { @Override public void actionPerformed(ActionEvent e) { boolean moved = false; for (Direction direction : Direction.values()) { if (directionMap.get(direction)) { playerX += STEP * direction.getXDirection(); playerY += STEP * direction.getYDirection(); moved = true; } } if (moved) { int x = playerX - 2 * STEP; int y = playerY - 2 * STEP; int w = playerImage.getWidth() + 4 * STEP; int h = playerImage.getHeight() + 4 * STEP; MoveIcon.this.repaint(x, y, w, h); // !! repaint just the player } } } private static void createAndShowUI() { JFrame frame = new JFrame("MoveIcon"); frame.getContentPane().add(new MoveIcon()); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.pack(); frame.setLocationRelativeTo(null); frame.setVisible(true); } public static void main(String[] args) { java.awt.EventQueue.invokeLater(new Runnable() { @Override public void run() { createAndShowUI(); } }); } } 

Thanks.

Answer 1

The simplest way might be something like this:

 import javax.swing.JFrame; public class TestBackgroudMethod { public static void main(final String[] args) { MyBackgroudMethod thread = new MyBackgroudMethod(); thread.setDaemon(true); thread.start(); java.awt.EventQueue.invokeLater(new Runnable() { public void run() { JFrame jFrame = new JFrame(); jFrame.setSize(200, 200); jFrame.setVisible(true); } }); } public static class MyBackgroudMethod extends Thread { @Override public void run() { while (true) { System.out.println("Executed!"); try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } } } } 

Edit

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Added sample with a swing worker:

 import javax.swing.JFrame; import javax.swing.SwingWorker; public class TestBackgroudMethod { public static void main(final String[] args) { new SwingBackgroupWorker().execute(); java.awt.EventQueue.invokeLater(new Runnable() { public void run() { JFrame jFrame = new JFrame(); jFrame.setSize(200, 200); jFrame.setVisible(true); } }); } public static class SwingBackgroupWorker extends SwingWorker<Object, Object> { @Override protected Object doInBackground() throws Exception { while (true) { java.awt.EventQueue.invokeLater(new Runnable() { public void run() { System.out.println("executed"); // here the swing update } }); try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } } } } 

Answer 2

"SWING is not thread safe," as you can see in the jar of Java documents.

The best way is to use the SwingWorker class . It provides functionality for calculating results or performing tasks that have a long lead time.