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More Java Techniques 759

BD6

Differences Between Applets and Applications ............................................

For the most part, programming a Java applet is no different from programming a stand-

alone application. In fact, it is possible to write a Java program that is both an application

and an applet. The differences between applet and application program can be summed

up as follows:

• For security reasons, applets cannot access files. It is obvious that you would not
  want a Web page snooping around on your hard disk, uploading your personal
  financial information, or deleting essential system files.


• An applet does not need a mainmethod. Because the execution of an applet is con-
  trolled by the browser it is running in, there is no need for main. If a program is
  designed to be both applet and application, it will have a main, but this method will
  be ignored when the program is running as an applet.


• Applet programming is a little simpler than application programming because the
  browser that the applet runs in takes care of some details, such as sizing and posi-
  tion the program window—things that a stand-alone application has to do for itself.


• Console input/output is meaningless for an applet.

Understanding the Structure of an Applet ....................................................

To get started with applets, look at Listing B6.7. This is not a real applet, but rather the

bare skeleton of an applet. The analysis that follows explains the various parts.

LISTINGB6.7 applet.java. The skeleton of a Java applet

1: import java.applet.Applet;

2:

3: public class AppletTest extends Applet {

4:

5: public void init() {}

6:

7: public void start() {}

8:

9: public void stop() {}

10:

11: public void destroy() {}

12:

13: public void paint() {}

14: }

Line 1: All applets must import java.applet.Appletin addition to any other

classes they need.

ANALYSIS

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