Processing: Creative Coding and Computational Art

Figure 6-24. End cap variation example
Running this code should give you a clear sense of the differences between the end cap
styles. These caps become a more significant concern as you begin to join lines into more
complex structures. However, before you do that, let’s review some of the code in the last
example.
The line int[]caps = {ROUND, PROJECT, SQUARE}; declares and initializes an array of type
int, and fills the index positions [0], [1], and [2] with the three constants ROUND,
PROJECT, and SQUARE. I discussed arrays in detail in Chapter 3. As a review, arrays are data
structures that hold multiple variables of any type. All the elements in an array need to be
of the same data type. To access an item stored in an array, you use an index number
placed between brackets, directly to the right of the array name, as in caps[0]. Arrays are
zero-indexed, meaning that the first position in the array is 0, not 1. The three end cap
styles, ROUND, PROJECT, and SQUARE, which look like strings, are actually immutable
(unchangeable) integer constants. Specifying an unchanging value as a constant and using
all uppercase letters in naming it are common programming approaches. In Java, the keyword
final is used to specify that a variable’s value is immutable. To find the corresponding
int values for the constants, run the following example:
println("ROUND = " + ROUND);
println("SQUARE = " + SQUARE);
println("PROJECT = " + PROJECT);
// uncomment the next line to generate a semantic error.
//ROUND = 27;
Now, to prove that you can’t change a constant’s value, uncomment the last line of the
code and run the sketch again, which should generate a compiler error telling you can’t
assign another value to ROUND.
Processing has a ton of constants defined in the language that work the same way. Each
constant is usually assigned an integer value (but not always). Mostly, constants add meaning
to the coding process. Isn’t it easier to remember the cap style ROUND than the number
2? You can see Processing’s constants at http://dev.processing.org/source/index.
cgi/trunk/processing/core/src/processing/core/PConstants.java?view=markup.
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