ClockDemo.java Source code

Introduction

Here is the source code for ClockDemo.java

Source

//File: applet.html
/*
    
<applet code="ClockDemo.class"
   codebase="."
   width=150 height=20>
</applet>
    
*/
///
/*
 * Copyright (c) 2000 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 2nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book (recommended),
 * visit http://www.davidflanagan.com/javaexamples2.
 */

import java.applet.Applet;
import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.Label;
import java.text.DateFormat;
import java.util.Date;

/**
 * This applet displays the time, and updates it every second
 */
public class ClockDemo extends Applet implements Runnable {
    Label time; // A component to display the time in

    DateFormat timeFormat; // This object converts the time to a string

    Thread timer; // The thread that updates the time

    volatile boolean running; // A flag used to stop the thread

    /**
     * The init method is called when the browser first starts the applet. It
     * sets up the Label component and obtains a DateFormat object
     */
    public void init() {
        time = new Label();
        time.setFont(new Font("helvetica", Font.BOLD, 12));
        time.setAlignment(Label.CENTER);
        setLayout(new BorderLayout());
        add(time, BorderLayout.CENTER);
        timeFormat = DateFormat.getTimeInstance(DateFormat.MEDIUM);
    }

    /**
     * This browser calls this method to tell the applet to start running. Here,
     * we create and start a thread that will update the time each second. Note
     * that we take care never to have more than one thread
     */
    public void start() {
        running = true; // Set the flag
        if (timer == null) { // If we don't already have a thread
            timer = new Thread(this); // Then create one
            timer.start(); // And start it running
        }
    }

    /**
     * This method implements Runnable. It is the body of the thread. Once a
     * second, it updates the text of the Label to display the current time
     */
    public void run() {
        while (running) { // Loop until we're stopped
            // Get current time, convert to a String, and display in the Label
            time.setText(timeFormat.format(new Date()));
            // Now wait 1000 milliseconds
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
            }
        }
        // If the thread exits, set it to null so we can create a new one
        // if start() is called again.
        timer = null;
    }

    /**
     * The browser calls this method to tell the applet that it is not visible
     * and should not run. It sets a flag that tells the run() method to exit
     */
    public void stop() {
        running = false;
    }

    /**
     * Returns information about the applet for display by the applet viewer
     */
    public String getAppletInfo() {
        return "Clock applet Copyright (c) 2000 by David Flanagan";
    }
}