如何在程序结束前让方法在后台持续运行？
我想知道，如何让方法在后台运行。 即。 程序启动时会启动此方法并继续执行其语句，直到程序关闭。 对于前者 假设我有一个方法“gravity（）”，它在程序运行时不断递减某个值。 现在我尝试使用以下程序，其中我试图在没有按下按键的情况下向下拉公爵（重力）。 但是没有发生。
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://sofzh.miximages.com/java/Bullfight.jpg"; private static final String IMAGE_PATH_PLAYER = "http://sofzh.miximages.com/java/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 directionMap = new HashMap(); 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(); } }); } } 谢谢。
用最简单的方法，你可以这样：
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(); } } } } }
编辑
使用swing worker添加样本：
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 { @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(); } } } } }
您可能已经在Java Docs中看到过“SWING不是线程安全的”。
最好的方法是使用SwingWorker类 。 它提供了计算具有较长执行时间的任务的结果或性能的function。