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
    • Creating Arrays
    • Using Arrays
    • Multidimensional Arrays
    • Sorting an Array
    • Workshop: Array of Prizes, Indeed
    • Summary
    • Q&A
    • Quiz
    • Activities
  • 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
  • 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

Multidimensional Arrays

The arrays you have been introduced to thus far in the hour all have one dimension, so you can retrieve an element using a number ranging from 0 to the largest element number in the array. Some types of information require more dimensions to store adequately as arrays. An example would be the (x,y) coordinate system. If you needed to store a list of x and y coordinates that have a point marked on them, you could use a two-dimensional array. One dimension of the array could store the x coordinate, and the other dimension could store the y coordinate.

To create an array that has two dimensions, you must use an additional set of square brackets when creating and using the array. Consider the following:

boolean[][] selectedPoint = new boolean[50][50]; 
selectedPoint[4][13] = true; 
selectedPoint[7][6] = true; 
selectedPoint[11][22] = true; 

This example creates an array of Boolean values called selectedPoint. The array has 50 elements in its first dimension and 50 elements in its second dimension, so there are 2,500 individual array elements that can hold values (50 multiplied by 50). When the array is created, each element is given the default value of false. Three elements are then given the value of true: a point at the (x,y) position of (4,13), one at (7,6), and one at (11,22).

Arrays can have as many dimensions as you need, but keep in mind that they take up a lot of memory if they're extremely large. Creating the 50 x 50 selectedPoint array was equivalent to creating 2,500 individual variables.

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