Processing: Creative Coding and Computational Art

PROCESSING: CREATIVE CODING AND COMPUTATIONAL ART
84
system, which I’ll discuss shortly. Arrays are a little difficult to get your head around at first,
but they are absolutely critical to coding, and you’ll be using them lots throughout the
book. So if some of this explanation feels a bit abstract, don’t worry—you’ll be revisiting
these concepts again and again.
Arrays don’t have a default data type, but rather are declared with a data type just like
variables are. Following is an example of an array declaration:
int[] xpos;
The declaration is done the way you’d declare a regular int variable, with the addition of
the two brackets. Here are two more array declarations:
float[] xspeed;
String[] names;
You see the pattern—the type comes first, then the brackets and then the identifier or
name of the array. You’ll notice in the two declaration lines that I wrote “float” in all lowercase,
but “String” with an initial cap. This was not an arbitrary decision on my part; float
is a primitive data type and needs to be all lowercase. String is the name of a class, and
the convention is to name a class with an initial cap. I’ll be covering classes later in the
book, but for now you can think of a class as representing a unique data type—which you
can use when you declare a variable, or in this case an array.
Arrays can be any size (actually as large as the int data type, which is big enough) and
hold any legal type. However, once they are declared, their type cannot change, and once
they are initialized, their size cannot change. Therefore, if I declare
float[] xspeed;
then the xspeed array can now only hold values of type float (real numbers). Here’s how
to initialize the xspeed array:
xspeed = new float[100];
The keyword new reserves space in memory for the array. You‘ll be using the keyword new
a lot more when we get to OOP.
Now the xspeed array has 100 places in memory reserved for float values. Its size, like its
data type, is now immutable, meaning that it can’t be changed. The array now has space in
the computer’s memory reserved for it, although it still doesn’t have any specific values
assigned to those 100 places. The two lines can be put together into one declaration and
initialization statement:
float[] xspeed = new float[100];
Here are a few more examples of declaring and initializing arrays:
int[] items = new int[50];
String[] itemNames = new String[10000];
Object[] obs = new Object[0];