Processing: Creative Coding and Computational Art

Variables
Variables are essential to programming, and it is hard to imagine coding anything without
them. In Processing and Java, there are two types of variables: primitive variables and
object reference variables. The major differences between these two categories of variables
are the kind of data they can be associated with and how this data is stored and referenced
in memory. I’m only going to cover primitive variables here; I’ll discuss object
reference variables when I cover OOP in Chapter 8.
A primitive variable is a simply a name assigned a specific value in memory that you can
recall and change. Here are a couple of examples of primitive variables:
int age = 6;
String name = "Ian";
boolean isABoy = true;
The first part of each of the statements (int, String, and boolean) declares what type of
primitive data the variable can hold: int holds integers, String holds words, and boolean
holds true or false. The next part (age, name, and isABoy) is the identifier of the variable,
and the last part is the actual value (6, "Ian", and true) assigned to the variable.
Variable names in Processing and Java are case sensitive, meaning that xSpeed is a different
variable than xspeed. A variable’s name is created by the coder and needs to be a legal
identifier, which was described previously. Regardless of whether you are naming a primitive
variable, object reference variable, function, method, class, or object, the same legal
identifier–naming rules apply. There are also some reserved keywords that you should
avoid using when naming things. The reserved keywords can be found here: http://
java.sun.com/docs/books/tutorial/java/nutsandbolts/_keywords.html. In addition, I
would also strongly recommend not naming your custom variables, functions, objects, and
so forth with any of the built-in function names in Processing; it will lead to, at best, unexpected
results.
When I initially create a variable by writing int ballCount, I am not yet specifying a specific
value to be assigned to the variable, but only letting the computer know what type of
data is allowed to be assigned to the variable (in this case, an integer). Every variable must
be associated with a data type. Some common primitive data types in Processing are int,
float, char, and boolean. Data types tell the variables what they can or can’t do, and also
how much memory should be allocated for them. For example, a boolean type variable
can only hold the values true or false, requiring only 1 bit of memory to store either a
single 0 (false) or a 1 (true). It would be a waste of memory to store it any other way. A
byte can hold a number between –128 to 127 (that’s 256 different possible values), which
requires 8 bits, or 1 byte, of memory.
CODE GRAMMAR 101
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