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
    • Creating Variables
    • Creating Class Variables
    • Creating Behavior with Methods
    • Putting One Class Inside Another
    • Using the this Keyword
    • Workshop: Using Class Methods and Variables
    • Summary
    • Q&A
    • Quiz
    • Activities
  • 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
  • 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

Q&A

1. Can constructor methods send back a value like other methods?

   No, because there's no way to receive that value. Unlike other methods that can be used as part of an equation, the argument of a method, or other statements, constructors are only handled in response to a new statement. There's no way for that statement to receive a value that would be sent by the method.

2. Do you have to create an object to use class variables or methods?

   Because class variables and methods aren't associated with a specific object, you don't need to create an object solely for the purpose of using them. The use of the Integer. parseInt() method is an example of this because you don't have to create a new Integer object just to convert a string to an int value.

3. Is there a list of all the built-in methods that Java supports?

   Sun offers full documentation for all classes in the Java language, including all the public methods you can use. The documentation is in HTML format, so you can browse easily through the classes to see what methods and variables they include. Visit the Java 2 version 1.4 documentation Web page at http://java.sun.com/j2se/1.4/docs/api. During the preparation of this book, I spent enough time at this part of Sun's Web site to qualify for California residency.

4. When I run the VirusLook application without an argument, the program crashes with an ArrayIndexOutOfBoundsException error. What can I do to correct this?

   This error occurs because of the effort to call the Integer.parseInt() method with a null string as the value of arguments[0]. One solution would be to test the value of arguments[0] with an if statement and call Integer.parseInt() only if arguments[0] is not null. This would require a default value for the numViruses variable. Arguments often require some kind of testing to make sure they have acceptable values before you use them.

5. What's the difference between the Integer object and the int variable type?

   The first is an object, and the second is a simple variable type. Each of the variable types, such as char, int, and float, has a corresponding object. The object is used when you want to make use of an object's methods or treat the variable like an object. Because an Integer object can do things in a program that the int variable type cannot, it is convenient to have both.