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【Java】简单秒表

作者:Dezai.CN / 发布于2011/7/13/ 821

这是一个简单的秒表。看起来很简单，但是这里有一个设计上的问题。一般初学者会创建一个循环的线程讲一个整数叠加，该线程隔一段时间暂停一下，比如暂停 10 毫秒，然后往这个整数上加 10。这样设计的问题在于，线程的暂停和继续，以及计数和显示都是要花费时间的。所以这样的程序运行越久，误差就会越大。下面这个例子就是经过改良的，能够将时间误差维持在极低的水平上。

import javax.swing.*;
import java.awt.HeadlessException;
import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

/**
* 小小的计时器
*/
public class TimerFrame extends JFrame {

 private static final String INITIAL_LABEL_TEXT = "00:00:00 000";

 // 计数线程
 private CountingThread thread = new CountingThread();

 // 记录程序开始时间
 private long programStart = System.currentTimeMillis();

 // 程序一开始就是暂停的
 private long pauseStart = programStart;

 // 程序暂停的总时间
 private long pauseCount = 0;

 private JLabel label = new JLabel(INITIAL_LABEL_TEXT);

 private JButton startPauseButton = new JButton("开始");

 private JButton resetButton = new JButton("清零");

 private ActionListener startPauseButtonListener = new ActionListener() {
 public void actionPerformed(ActionEvent e) {
 if (thread.stopped) {
 pauseCount += (System.currentTimeMillis() - pauseStart);
 thread.stopped = false;
 startPauseButton.setText("暂停");
 } else {
 pauseStart = System.currentTimeMillis();
 thread.stopped = true;
 startPauseButton.setText("继续");
 }
 }
 };

 private ActionListener resetButtonListener = new ActionListener() {
 public void actionPerformed(ActionEvent e) {
 pauseStart = programStart;
 pauseCount = 0;
 thread.stopped = true;
 label.setText(INITIAL_LABEL_TEXT);
 startPauseButton.setText("开始");
 }
 };

 public TimerFrame(String title) throws HeadlessException {
 super(title);
 setDefaultCloseOperation(EXIT_ON_CLOSE);
 setLocation(200, 200);
 setResizable(false);

 setupBorder();
 setupLabel();
 setupButtonsPanel();

 startPauseButton.addActionListener(startPauseButtonListener);
 resetButton.addActionListener(resetButtonListener);

 thread.start(); // 计数线程一直就运行着
 }

 // 为窗体面板添加边框
 private void setupBorder() {
 JPanel contentPane = new JPanel(new BorderLayout());
 contentPane.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));
 this.setContentPane(contentPane);
 }

 // 配置按钮
 private void setupButtonsPanel() {
 JPanel panel = new JPanel(new FlowLayout());
 panel.add(startPauseButton);
 panel.add(resetButton);
 add(panel, BorderLayout.SOUTH);
 }

 // 配置标签
 private void setupLabel() {
 label.setHorizontalAlignment(SwingConstants.CENTER);
 label.setFont(new Font(label.getFont().getName(), label.getFont().getStyle(), 40));
 this.add(label, BorderLayout.CENTER);
 }

 // 程序入口
 public static void main(String[] args) {
 try {
 UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
 } catch (Exception e) {
 e.printStackTrace();
 }

 TimerFrame frame = new TimerFrame("小小计时器");
 frame.pack();
 frame.setVisible(true);
 }

 private class CountingThread extends Thread {

 public boolean stopped = true;

 private CountingThread() {
 setDaemon(true);
 }

 @Override
 public void run() {
 while (true) {
 if (!stopped) {
 long elapsed = System.currentTimeMillis() - programStart - pauseCount;
 label.setText(format(elapsed));
 }

 try {
 sleep(17); // 使时钟显得更乱
 } catch (InterruptedException e) {
 e.printStackTrace();
 System.exit(1);
 }
 }
 }

 // 将毫秒数格式化
 private String format(long elapsed) {
 int hour, minute, second, milli;

 milli = (int) (elapsed % 1000);
 elapsed = elapsed / 1000;

 second = (int) (elapsed % 60);
 elapsed = elapsed / 60;

 minute = (int) (elapsed % 60);
 elapsed = elapsed / 60;

 hour = (int) (elapsed % 60);

 return String.format("%02d:%02d:%02d %03d", hour, minute, second, milli);
 }
 }
}
</div>

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