Processing: Creative Coding and Computational Art

PROCESSING: CREATIVE CODING AND COMPUTATIONAL ART
680
Composite
The Composite section includes data types used to store object references (the memory
addresses I mentioned in the primitive data type discussion). The three composite types
Array, Object, and String can each hold multiple pieces of data.
Arrays are collections of any other data type, referenced by a single variable name. Arrays
can only hold one data type at a time, but lots of it. I cover arrays in detail in Chapter 3.
Objects are the main units in object-oriented programming. An object is an instance of a
class and includes copies of the properties and methods defined within the class. Objects
are covered in much greater depth in Chapter 8 in the discussion of object-oriented programming
(OOP).
Strings are kind of like arrays that only hold characters (e.g., letters). There are two ways
to create String objects in Processing and Java (which is confusing):
and
String s1 = "hello";
String s2 = new String("hello");
The first way looks like a normal primitive declaration, like you would use to declare an
int (int count = 3;), a float (float speed = .5;), and so on. The second way looks like
standard object creation, called instantiation, which uses the standard object-oriented syntax
ClassType variableName = new ClassType();. Based on what I’ve told you about
data types up to this point in the book, this may not make sense. How can a string represent
both a primitive data type and also a reference (composite) data type? Well, in truth,
there is no primitive String data type in Java or Processing; you’re always creating a
String object. The shortcut approach String s1 = "hello"; internally creates a String
object from the literal (the word in quotes). This is all fine and good, as well as probably a
little overly technical. However, if you eventually find yourself needing to compare two
strings and test them for equality, these two different string-creation approaches have
some confusing (and probably annoying) differences.
As an example, run the following:
String s1 = "hello";
String s2 = new String("hello");
println(s1 == s2);
String s3 = "goodbye";
String s4 = "goodbye";
println(s3 == s4);
The output tells you that s1 and s2 are not equal, but s3 and s4 are. Even though the two
values being compared in each comparison are the same (hello and hello and goodbye
and goodbye), the output is different because of the different ways the strings were created.
I won’t bore you further with why this occurs, but you can read more about it here:
http://java.about.com/library/weekly/aa_strings1.htm. Be sure to check the second