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
    • How Object-Oriented Programming Works
    • Objects in Action
    • What Objects Are
    • Understanding Inheritance
    • Building an Inheritance Hierarchy
    • Converting Objects and Simple Variables
    • Workshop: Creating an Object
    • Summary
    • Q&A
    • Quiz
    • Activities
  • 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
  • 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

Understanding Inheritance

One of the biggest advantages to using object-oriented programming is inheritance, which is the way one object can inherit behavior and attributes from other objects that are similar to it.

When you start creating objects for use in other programs, you will find that some new objects you want are a lot like other objects that have already been developed. For example, if David Lightman does not run afoul of the law because of his ATM scheme, he might want to create an object that can handle error correction and other advanced modem features that weren't around back in 1983 when WarGames was released.

Lightman could create a new ErrorCorrectionModem object by copying the statements of the Modem object and revising them. However, if most of the behavior and attributes of ErrorCorrectionModem are the same as those of Modem, this is a lot of unnecessary work. It also means that Lightman will have to maintain two separate programs if something needs to be changed or debugged later. Through inheritance, a programmer can create a new class of objects by defining only how it is different from an existing class. Lightman could make ErrorCorrectionModem inherit from Modem, and all he would have to write are the things that make error-correction modems different than previous modems.

The way a class of objects inherits from another class is through the extends statement. The following is a skeleton of an ErrorCorrectionModem class that inherits from the Modem class:

class ErrorCorrectionModem extends Modem { 
    // program goes here 
} 

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