Java Tutorial/Thread/Thread Swing

Create a thread to update Swing

1. implements the Runnable interface.
2. extends the Thread class.

The threads must also create a run() method that accepts no arguments and returns void. The run() method is called when the thread is started. A thread is started by invoking the Thread.start() method. It can be stopped by returning from the run() method.

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Clock extends JPanel implements Runnable {
  Thread thread = null;
  SimpleDateFormat formatter = new SimpleDateFormat("s", Locale.getDefault());
  Date currentDate;
  int xcenter = 100, ycenter = 100, lastxs = 0, lastys = 0, lastxm = 0, lastym = 0, lastxh = 0,
      lastyh = 0;
  private void drawStructure(Graphics g) {
    g.setFont(new Font("TimesRoman", Font.PLAIN, 14));
    g.setColor(Color.blue);
    g.drawOval(xcenter - 50, ycenter - 50, 100, 100);
    g.setColor(Color.darkGray);
    g.drawString("9", xcenter - 45, ycenter + 3);
    g.drawString("3", xcenter + 40, ycenter + 3);
    g.drawString("12", xcenter - 5, ycenter - 37);
    g.drawString("6", xcenter - 3, ycenter + 45);
  }
  public void paint(Graphics g) {
    int xhour, yhour, xminute, yminute, xsecond, ysecond, second, minute, hour;
    drawStructure(g);
    currentDate = new Date();
    
    formatter.applyPattern("s");
    second = Integer.parseInt(formatter.format(currentDate));
    formatter.applyPattern("m");
    minute = Integer.parseInt(formatter.format(currentDate));
    formatter.applyPattern("h");
    hour = Integer.parseInt(formatter.format(currentDate));
    xsecond = (int) (Math.cos(second * 3.14f / 30 - 3.14f / 2) * 45 + xcenter);
    ysecond = (int) (Math.sin(second * 3.14f / 30 - 3.14f / 2) * 45 + ycenter);
    xminute = (int) (Math.cos(minute * 3.14f / 30 - 3.14f / 2) * 40 + xcenter);
    yminute = (int) (Math.sin(minute * 3.14f / 30 - 3.14f / 2) * 40 + ycenter);
    xhour = (int) (Math.cos((hour * 30 + minute / 2) * 3.14f / 180 - 3.14f / 2) * 30 + xcenter);
    yhour = (int) (Math.sin((hour * 30 + minute / 2) * 3.14f / 180 - 3.14f / 2) * 30 + ycenter);
    // Erase if necessary, and redraw
    g.setColor(Color.lightGray);
    if (xsecond != lastxs || ysecond != lastys) {
      g.drawLine(xcenter, ycenter, lastxs, lastys);
    }
    if (xminute != lastxm || yminute != lastym) {
      g.drawLine(xcenter, ycenter - 1, lastxm, lastym);
      g.drawLine(xcenter - 1, ycenter, lastxm, lastym);
    }
    if (xhour != lastxh || yhour != lastyh) {
      g.drawLine(xcenter, ycenter - 1, lastxh, lastyh);
      g.drawLine(xcenter - 1, ycenter, lastxh, lastyh);
    }
    
    g.setColor(Color.darkGray);
    g.drawLine(xcenter, ycenter, xsecond, ysecond);
   
    g.setColor(Color.red);
    g.drawLine(xcenter, ycenter - 1, xminute, yminute);
    g.drawLine(xcenter - 1, ycenter, xminute, yminute);
    g.drawLine(xcenter, ycenter - 1, xhour, yhour);
    g.drawLine(xcenter - 1, ycenter, xhour, yhour);
    lastxs = xsecond;
    lastys = ysecond;
    lastxm = xminute;
    lastym = yminute;
    lastxh = xhour;
    lastyh = yhour;
  }
  public void start() {
    if (thread == null) {
      thread = new Thread(this);
      thread.start();
    }
  }
  public void stop() {
    thread = null;
  }
  public void run() {
    while (thread != null) {
      try {
        Thread.sleep(100);
      } catch (InterruptedException e) {
      }
      repaint();
    }
    thread = null;
  }
  public void update(Graphics g) {
    paint(g);
  }
  public static void main(String args[]) {
    JFrame window = new JFrame();
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setBounds(30, 30, 300, 300);
    Clock clock = new Clock();
    window.getContentPane().add(clock);
    window.setVisible(true);
    clock.start();
  }
}