Think Java

Chapter 8. Arrays

Up to this point, the only variables we have used were for individual values such as numbers or strings. In this chapter, we’ll learn how to store multiple values of the same type using a single variable. This language feature will enable you to write programs that manipulate larger amounts of data.

Creating Arrays

An array is a sequence of values; the values in the array are called elements. You can make an array of ints, doubles, or any other type, but all the values in an array must have the same type.

To create an array, you have to declare a variable with an array type and then create the array itself. Array types look like other Java types, except they are followed by square brackets ([]). For example, the following lines declare that counts is an “integer array” and values is a “double array”:

int[] counts;
double[] values;

To create the array itself, you have to use the new operator, which we first saw in “The Scanner Class”:

counts = new int[4];
values = new double[size];

The first assignment makes count refer to an array of four integers. The second makes values refer to an array of double, where the number of elements in values depends on the value of size.

Of course, you can also declare the variable and create the array in a single line of code:

int[] counts = new int[4];
double[] values = new double[size];

You can use any integer expression for the size of an array, as long as the value is nonnegative. If you try to create an array with –4 elements, for ...