Info Tech Guide

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've seen an example of arrays already, in the main method of the "Hello World!" application. This section discusses arrays in greater detail.

Each item in an array is called an element, and each element is accessed by its numerical index. As shown in the above 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 it, and prints each value to standard output.

class ArrayDemo {

public static void main(String[] args) {

int[] anArray; // declares an array of integers

anArray = new int[10]; // allocates memory for 10 integers

anArray[0] = 100; // initialize first element

anArray[1] = 200; // initialize second element

anArray[2] = 300; // etc.

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 the Java programming language, a multidimensional array is simply an array whose components are themselves arrays. This is unlike arrays in C or Fortran. A consequence of this is that the rows are allowed to vary in length, as shown in the following MultiDimArrayDemo program:

class MultiDimArrayDemo {

public static void main(String[] args) {

String[][] names = {{"Mr. ", "Mrs. ", "Ms. "},

{"Smith", "Jones"}};

System.out.println(names[0][0] + names[1][0]); //Mr. Jones

System.out.println(names[0][2] + names[1][1]); //Ms. Smith

}

}

The output from this program is:

Mr. Jones

Ms. Smith