16.1: Creating Arrays

Last updated
Save as PDF

Page ID: 15256

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

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 Section 3.2:

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 example, you will get a NegativeArraySizeException. An array with zero elements is allowed, and there are special uses for such arrays that we’ll see later on.