Sams Teach Yourself Java 2 in 24 Hours

By Rogers Cadenhead

• Table of Contents
  • Copyright
  • About the Author
  • About the Technical Editor
  • Acknowledgments
  • We Want to Hear from You!
  • Reader Services
  • Introduction
  • Hour 1. Becoming a Programmer
  • Hour 2. Writing Your First Program
  • Hour 3. Vacationing in Java
  • Hour 4. Understanding How Java Programs Work
  • Part II: Learning the Basics of Programming
  • Hour 5. Storing and Changing Information in a Program
  • Hour 6. Using Strings to Communicate
  • Hour 7. Using Conditional Tests to Make Decisions
  • Hour 8. Repeating an Action with Loops
  • Part III: Working with Information in New Ways
  • Hour 9. Storing Information with Arrays
  • Hour 10. Creating Your First Object
  • Hour 11. Describing What Your Object Is Like
  • Hour 12. Making the Most of Existing Objects
  • Part IV: Programming a Graphical User Interface
  • Hour 13. Building a Simple User Interface
  • Hour 14. Laying Out a User Interface
  • Hour 15. Responding to User Input
  • Hour 16. Building a Complex User Interface
  • Part V: Creating Multimedia Programs
  • Hour 17. Creating Interactive Web Programs
  • Hour 18. Handling Errors in a Program
  • Hour 19. Creating a Threaded Program
    • Threads
    • Working with Threads
    • Starting with init()
    • Catching Errors as You Set Up URLs
    • Handling Screen Updates in the paint() Method
    • Starting the Thread
    • Handling Mouse Clicks
    • Workshop: Revolving Links
    • Summary
    • Q&A
    • Quiz
    • Questions
    • Activities
  • Hour 20. Reading and Writing Files
  • Part VI: Creating Multimedia Programs
  • Hour 21. Using Fonts and Color
  • Hour 22. Playing Sound Files
  • Hour 23. Working with Graphics
  • Hour 24. Creating Animation
  • Part VII: Appendixes
  • Appendix A. Tackling New Features of Java 2 Version 1.4
  • Appendix B. Using the Java 2 Software Development Kit
  • Appendix C. Programming with the Java 2 Software Development Kit
  • Appendix D. Using Sun ONE Studio
  • Appendix E. Where to Go from Here: Java Resources
  • Appendix F. This Book's Web Site

Handling Mouse Clicks

The last thing to take care of in the Revolve applet is event-handling: Whenever a user clicks the Go button, the Web browser should open the Web site that is listed. This is done with a method called actionPerformed(). The actionPerformed() method is called whenever the button is clicked.

The following is the actionPerformed() method of the Revolve applet:

public void actionPerformed(ActionEvent evt) { 
    if (runner != null) { 
        runner = null; 
    } 
    AppletContext browser = getAppletContext(); 
    if (pageLink[current] != null) 
        browser.showDocument(pageLink[current]); 
} 

The first thing that happens in this method is that the runner thread is stopped in the same way it was stopped in the applet's stop() method. The next statement creates a new AppletContext object called browser.

An AppletContext object represents the environment in which the applet is being presented—in other words, the page it's located on and the Web browser that loaded the page.

The showDocument() method of this object is called with a single argument: a URL object representing a World Wide Web address. If the page represented by pageLink[current] is a valid address, showDocument() is used to request that the browser load the page.

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