Arrays

An array allows you to have many values, without having to declare a separate variable to hold each one.

All the values in an array must be of the same type; this is called the base type of the array. The array itself is said to be of type "array of base type." For example, if the base type is int, then the array type is "array of int."

The syntax for declaring an array is:

accessType optionalStatic baseType[] arrayName;

where

• accessType is one of the access types public, protected, omitted (meaning "package"), or private,
• optionalStatic is either the keyword static or is omitted (meaning "instance"),
• baseType is the type of value permitted in the array; if the type is a class or interface name, then values of any subclass of that class are also permitted; and
• arrayName is a name chosen by the programmer to use when referring to the array.

For example,

public int scores[];

Notice that the length of the array (the number of values it can hold) is not part of the declaration. Rather, it is part of the value assigned to the array. For example, an array value might be

new int[35]

This is not a statement by itself, but an expression that creates a new array of the given length. It can be used as an initial value of the array,

public int scores[] = new int[35];

or a value can be assigned to the variable scores at some later time:

scores = new int[43];

Either way, this is called defining the array, as opposed to declaring the array. An array variable that has been declared but not defined has the special value null, and there isn't much you can do with such a variable.

You access the individual values in an array by indexing into it, using the syntax arrayName[index]. The first value in the array has index 0 (zero); the last value in the array has the index arrayName.length - 1. To access each element in turn, you would typically use a for loop.

Despite having a special syntax, strings are objects.

The values in an array can themselves be arrays. There is a special syntax for this, as in the following examples:

public double elevation[][]; // declaration

elevation = new double[50][75]; // defines an array with 50 rows and 75 columns

elevation[i][j + 1] = elevation[i][j] + 0.05; // using the array

These arrays are referred to as two-dimensional arrays. Arrays may have three, four, or even more dimensions.

The values in an array can themselves be arrays, but these arrays need not all be the same size. If they are of different sizes, the result is a ragged array. For example, the following code constructs a "triangular" array, in which each sub-array is larger than the one preceding it:

int[] triangle = new int[10];
for (int i = 0; i < triangle.length; i++) {
    triangle[i] = new int[i + 1];
}