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（）”，它在程序运行时连续减少某个值。 现在尝试使用以下程序，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://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();
}
});
}
}
谢谢。
答案 0 :(得分：5)
最简单的方法是，您可以这样：
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();
}
}
}
}
}
修改
为摇摆工作者添加样本：
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<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();
}
}
}
}
}
答案 1 :(得分：2)
“SWING不是线程安全的”，正如您在Java Docs中看到的那样。
最好的方法是使用SwingWorker class。它提供了计算执行时间较长的任务的结果或性能的功能。