怎样用java实现日期时钟“2004-3-15 16：42：15”？

Question

SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String str=format.format(new java.util.Date());
System.out.println(str);

Answer 1

给你一个完整的例子import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
import java.util.*;
import java.text.SimpleDateFormat;/* ComboBoxDemo2.java is a 1.4 application that requires no other files. */
public class ComboBoxDemo2 extends JPanel
                           implements ActionListener {
    static JFrame frame;
    JLabel result;
    String currentPattern;    public ComboBoxDemo2() {
        setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));
        String[] patternExamples = {
                 "dd MMMMM yyyy",
                 "dd.MM.yy",
                 "MM/dd/yy",
                 "yyyy.MM.dd G 'at' hh:mm:ss z",
                 "EEE, MMM d, ''yy",
                 "h:mm a",
                 "H:mm:ss:SSS",
                 "K:mm a,z",
                 "yyyy.MMMMM.dd GGG hh:mm aaa"
                 };        currentPattern = patternExamples[0];        //Set up the UI for selecting a pattern.
        JLabel patternLabel1 = new JLabel("Enter the pattern string or");
        JLabel patternLabel2 = new JLabel("select one from the list:");        JComboBox patternList = new JComboBox(patternExamples);
        patternList.setEditable(true);
        patternList.addActionListener(this);        //Create the UI for displaying result.
        JLabel resultLabel = new JLabel("Current Date/Time",
                                        JLabel.LEADING); //== LEFT
        result = new JLabel(" ");
        result.setForeground(Color.black);
        result.setBorder(BorderFactory.createCompoundBorder(
             BorderFactory.createLineBorder(Color.black),
             BorderFactory.createEmptyBorder(5,5,5,5)
        ));        //Lay out everything.
        JPanel patternPanel = new JPanel();
        patternPanel.setLayout(new BoxLayout(patternPanel,
                               BoxLayout.PAGE_AXIS));
        patternPanel.add(patternLabel1);
        patternPanel.add(patternLabel2);
        patternList.setAlignmentX(Component.LEFT_ALIGNMENT);
        patternPanel.add(patternList);        JPanel resultPanel = new JPanel(new GridLayout(0, 1));
        resultPanel.add(resultLabel);
        resultPanel.add(result);        patternPanel.setAlignmentX(Component.LEFT_ALIGNMENT);
        resultPanel.setAlignmentX(Component.LEFT_ALIGNMENT);        add(patternPanel);
        add(Box.createRigidArea(new Dimension(0, 10)));
        add(resultPanel);        setBorder(BorderFactory.createEmptyBorder(10,10,10,10));        reformat();
    } //constructor    public void actionPerformed(ActionEvent e) {
        JComboBox cb = (JComboBox)e.getSource();
        String newSelection = (String)cb.getSelectedItem();
        currentPattern = newSelection;
        reformat();
    }    /** Formats and displays today's date. */
    public void reformat() {
        Date today = new Date();
        SimpleDateFormat formatter =
           new SimpleDateFormat(currentPattern);
        try {
            String dateString = formatter.format(today);
            result.setForeground(Color.black);
            result.setText(dateString);
        } catch (IllegalArgumentException iae) {
            result.setForeground(Color.red);
            result.setText("Error: " + iae.getMessage());
        }
    }    /**
     * Create the GUI and show it.  For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Make sure we have nice window decorations.
        JFrame.setDefaultLookAndFeelDecorated(true);        //Create and set up the window.
        JFrame frame = new JFrame("ComboBoxDemo2");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        //Create and set up the content pane.
        JComponent newContentPane = new ComboBoxDemo2();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}

Answer 2

把下面代码Copy过去，可以直接运行的。import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.text.*;public class clockTest extends JFrame {
  JButton jButton1 = new JButton();
  BorderLayout borderLayout1 = new BorderLayout();
  JLabel t1=new JLabel("I am a clock");  public clockTest() {
    super("Clock Test");
    try {      jbInit();
      setSize(300,300);
      setVisible(true);
    }
    catch(Exception e) {
      e.printStackTrace();
    }
  }
  public static void main(String[] args) {
    clockTest clockTest = new clockTest();
  }
  private void jbInit() throws Exception {
    jButton1.setText("Start");
    jButton1.addActionListener(new clockTest_jButton1_actionAdapter(this));
    this.getContentPane().setLayout(borderLayout1);
    this.addWindowListener(new clockTest_this_windowAdapter(this));
    this.getContentPane().add(jButton1, BorderLayout.NORTH);
    this.getContentPane().add(t1,BorderLayout.SOUTH);
  }  void this_windowClosing(WindowEvent e) {
    System.exit(0);
  }  void jButton1_actionPerformed(ActionEvent e) {
    timeLabel a = new timeLabel(t1);
    a.start();
  }
}
class timeLabel extends Thread
{
  JLabel t2=new JLabel();
  public timeLabel(JLabel t1)
  {
    super();
    t2=t1;
  }  public void run()
  {
    while(true)
    {
    SimpleDateFormat format=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    String str=format.format(new java.util.Date());
    t2.setText(str);    try
    {
      this.sleep(1000);
    }
    catch(Exception ex)
    {
      ex.printStackTrace();
    }}
  }
}class clockTest_this_windowAdapter extends java.awt.event.WindowAdapter {
  clockTest adaptee;  clockTest_this_windowAdapter(clockTest adaptee) {
    this.adaptee = adaptee;
  }
  public void windowClosing(WindowEvent e) {
    adaptee.this_windowClosing(e);
  }
}class clockTest_jButton1_actionAdapter implements java.awt.event.ActionListener {
  clockTest adaptee;  clockTest_jButton1_actionAdapter(clockTest adaptee) {
    this.adaptee = adaptee;
  }
  public void actionPerformed(ActionEvent e) {
    adaptee.jButton1_actionPerformed(e);
  }
}