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

Creating Arrays

Arrays are variables that are grouped together under a common name. The term array should be familiar to you, though the meaning might not be so clear—think of a salesman showing off his array of fabulous cleaning products, or a game show with a dazzling array of prizes. Like variables, arrays are created by stating the type of the variable being organized into the array and the name of the array. The difference lies in the addition of the square bracket marks [ and ].

You can create arrays for any type of information that can be stored as a variable. For example, the following statement creates an array of string variables:

String[] naughtyChild; 

Here are two more examples:

int[] reindeerWeight; 
boolean[] hostileAirTravelNations; 

String niceChild[]; 

The previous examples create arrays, but they do not store any values in them initially. To do this, you must either use the new statement along with the variable type or store values in the array within { and } marks. You also must specify how many different items will be stored in the array. Each item in an array is called an element. The following statement creates an array and sets aside space for the values that it will hold:

int[] elfSeniority = new int[250]; 

This example creates an array of integers called elfSeniority. The array has 250 elements in it that can be used to store the months that each of Santa's elves has been employed at the Pole. If the rumors are true and Santa runs a union shop, this information is extremely important to keep track of.

When you create an array with the new statement, you must specify the number of elements. Each element of the array is given an initial value when it is set up with new; the value depends on the type of the array. All numeric arrays have the value 0, char arrays have the value '\0', and boolean arrays have the value false. A String array and all other objects are created with the initial value of null.

For arrays that are not extremely large, you can set up their initial values at the same time that you create them. The following example creates an array of strings and gives them initial values:

String[] reindeerNames = { "Dasher", "Dancer", "Prancer", "Vixen", 
    "Comet", "Cupid", "Donder", "Blitzen" }; 

The information that should be put into elements of the array is placed between { and } brackets, with commas separating each element. The number of elements in the array is not specified in the statement because it is set to the number of elements in the comma-separated list. Each element of the array in the list must be of the same type. The preceding example uses a string for each of the reindeer names.

Once the array is created, you cannot make more space and add another variable to the array. Even if you recall the most famous reindeer of all, you couldn't add "Rudolph" as the ninth element of the reindeerNames array. A Java compiler won't let poor Rudolph join in any reindeerNames.

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