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//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";
}
}
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