|
Chapter: Object
Oriented Programming
Creating a Class
As previously mentioned a class typically consists of method
definitions and various fields (which we also refer to as member
variables) that store information about the current state of the object
instantiated from the class. The term fields refers to variables that
are members of a particular class, and as a result are encapsulated
data that store information about the object itself and are sometimes
referred to in Processing as class data.
Typically in Processing creating a class is a four step process that
involves,
1)Class Name creation
2)Field declarations
3)Constructor creation
4)Method definitions
The structure of a class looks similar to setup() and draw() and user
defined functions, but since a class is not a function, but may contain
many functions (called methods) it's name is not followed by
parenthesis. An object variable name which we will have a look at
shortly, on the other hand is followed by parenthesis in order to
provide a means of communicating with the object's internal structure.
void setup(){
}
void draw(){
}
class ClassName{
}
As you can see a class definition usually finds it's place at the very
end of a sketch, this is sometimes referred to as an in-line class
definition. This simply emphasizes that the class is directly related
to the sketch that it is defined within. As defining a class at the end
of a sketch, after user defined functions, mouse and keyboard functions
etc can create a cluttered looking sketch Processing also provides us
with Tabs in which we can place additional code that will be compiled
with the sketch we are currently working on. You can create a new tab
by clicking the arrow pointing to the right on the far right of the PDE
and a fly-off menu relating to Tabs will appear.
The Tab
fly-off menu from the PDE
Processing will then ask you to provide a name for the new tab.
Creating a new
Tab
Once you supply a unique name and click OK Processing will create a new
blank Tab next to the original Tab. What has actually happened is that
Processing has created a new .pde file that has the name you specified
for the Tab that was just created. This new .pde file resides in the
same location as the sketch you are currently working on, as a result
it can access anything in the data folder that you can access from the
code of the original Tab. Although Processing has created another .pde
file this file is only part of a sketch. In a similar way that the
original pde file can be reliant on the contents of the data folder,
the new .pde file in the same location as the original .pde file can
also be reliant on the original .pde and the contents of the data
folder. As a result we refer to this collection of elements (i.e. pde
files, txt files, spreadsheets, images and anything else that is in the
data folder used in the sketch) collectively as the contents or
components of a sketch.
Using additional Tabs in a sketch provides us with a convenient
location for placing classes. This is useful because it emphasizes the
modular design of classes and clears the main .pde file from becoming
over-cluttered with code. Working with additional tabs is not
synonymous to working with multiple sketches. Multiple tabs are a means
of breaking up the current sketch you are working on into smaller
manageable portions of code. As a result when a sketch with multiple
Tabs is run all the code within all the Tabs of that sketch are
compiled together. This means that only one of the Tabs should have
setup() and draw() structures, the other Tabs should be used for class
definitions, user defined functions or other elements of a sketch that
exist outside of setup() and draw() structures.
|
|
Previous
