The Java Boutique: Introduction to Java Part 4: Data Types and Operators

Articles : JavaBoutique's Introduction to Java :
Data Types and Operators :

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Printing to Standard Output

Variables

- Data Types

- Declaring, Assigning, and Casting

- Variable Type Helper Objects

Arrays

List arrays (also known simply as "arrays" for short) take the concept of scalar variables to the next level. Whereas scalar variables associate one value with one variable name, list arrays associate one array name with a "list" of values.

Java has a built in array class that you can use to hold multiple values so long as those values are of the same data type.

In Java, arrays are fairly restrictive. For example, you may not change the size of an array once you have created it. To add elements to an array dynamically, for example, you actually have to create a new, larger array and copy the old array into the new one using arrayCopy() in the java.lang.System class.

For a dynamically resizable data structure, you may want to look to the Vector class in the java.util package. We'll talk more about Vectors later.

However, for cases in which you do not need to dynamically resize your data structure, arrays work great. Java provides a zero-based array that is defined much as variables are. You first declare what type of data will be stored in an array, give the array a name, and then define how large it is. Consider the following example:

int[] intArray = new int[50];

This array would hold 50 ints indexed from 0-49.

To get or set a value, you simply access it by its index in the array. For example, to fill an array with the number 0-49 and then print the value 49, you might use:

int[] intArray = new int[50];
for (int i = 0; i < 50; i++)
  {
  intArray[i] = i;
  }

for (int i = 0; i < 50; i++)
  {
  System.out.println("Value: " + intArray[i]);
  }

System.out.println(intArray[50]);

Java also allows you to define an array at time of initialization such as in the following example:

int[] intArray = {0,1,2,3,4};

Selena Sol contributes to the JavaBoutique's Introduction to Java. Selena curently works for Barclays Capital in London, one of the leading global investment banks in Europe and has worked as a software developer for the National Center for Human Genome research, Microline Software, Neuron Data, and Electric Eye in Singapore. Selena is perhaps best-known for creating the Public Domain Web Script Archive (Extropia) and writing several books on Web Programming (Perl, CGI, Java).
Email: selena@extropia.com

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