An array is a container object that holds a fixed number of values of a single type. The length of an array is established when the array is created. After creation, its length is fixed. You have seen an example of arrays already, in the main method of the "Hello World!" application. This section discusses arrays in greater detail.

An array of 10 elements.

Each item in an array is called an element, and each element is accessed by its numerical index. As shown in the preceding illustration, numbering begins with 0. The 9th element, for example, would therefore be accessed at index 8.

The following program, ArrayDemo, creates an array of integers, puts some values in the array, and prints each value to standard output.

class ArrayDemo {

    public static void main(String[] args) {

        // declares an array of integers

        int[] anArray;



        // allocates memory for 10 integers

        anArray = new int[10];

           

        // initialize first element

        anArray[0] = 100;

        // initialize second element

        anArray[1] = 200;

        // and so forth

        anArray[2] = 300;

        anArray[3] = 400;

        anArray[4] = 500;

        anArray[5] = 600;

        anArray[6] = 700;

        anArray[7] = 800;

        anArray[8] = 900;

        anArray[9] = 1000;



        System.out.println("Element at index 0: "

                           + anArray[0]);

        System.out.println("Element at index 1: "

                           + anArray[1]);

        System.out.println("Element at index 2: "

                           + anArray[2]);

        System.out.println("Element at index 3: "

                           + anArray[3]);

        System.out.println("Element at index 4: "

                           + anArray[4]);

        System.out.println("Element at index 5: "

                           + anArray[5]);

        System.out.println("Element at index 6: "

                           + anArray[6]);

        System.out.println("Element at index 7: "

                           + anArray[7]);

        System.out.println("Element at index 8: "

                           + anArray[8]);

        System.out.println("Element at index 9: "

                           + anArray[9]);

    }

} 

The output from this program is:

Element at index 0: 100

Element at index 1: 200

Element at index 2: 300

Element at index 3: 400

Element at index 4: 500

Element at index 5: 600

Element at index 6: 700

Element at index 7: 800

Element at index 8: 900

Element at index 9: 1000

In a real-world programming situation, you would probably use one of the supported looping constructs to iterate through each element of the array, rather than write each line individually as in the preceding example. However, the example clearly illustrates the array syntax. You will learn about the various looping constructs (for, while, and do-while) in the Control flow section.