Objects
September 28, 1998
OOP is based around the concept of
objects. Objects are little black boxes of functionality
that are fully independent of any code that references or
uses them.
Objects can be thought of as
exhibiting two characteristics. Objects have properties and
objects have methods.
Properties describe the qualities of
an object while methods specify the object's behavior.
The typical "introduction to objects"
chapter will give you an example something like this:
| The Cat Object |
| Properties |
Methods |
| Eye Color |
Can Purr |
| Number of legs |
Catches mice |
| Species |
Rips up the couch |
| Although this is
not a perfect analogy, sometimes when I am trying to figure
out what an object looks like, I think of objects in terms of
nouns, properties in terms of adjectives, and methods in
terms of verbs. |
However, let's consider a more
realistic object that you might have to deal with in your
code. Let's consider the HTML FORM "Select Box" object that
we discussed on Day One and which is shown below as a
reminder:
If you recall, a Select Box object
has several properties.
For one, Select Boxes have a SIZE
that corresponds to the number of visible selections.
Select Boxes also can be set to allow either multiple or
single selections. Finally, Select Boxes have a list of
OPTIONS that are tied to an administratively-defined
NAME.
Meanwhile, Select Boxes have
methods.
For example, a select box knows how
to create its popup list when a user clicks on the down
arrow. Also, if a user selects an item from the popup list,
the select box knows how to select that item. Further, the
Select Box knows how to close the popup box when a user
selects an item.
The table below presents a quick
reference to our select box object.
| The Select Box Object |
| Properties |
Methods |
| Size |
Open Drop Down Box |
| Selection Policy |
Select an Item |
| List of Items |
Close Drop Down Box |
Object-Oriented Programming
Introduction to Perl 5 | Table of Contents
Encapsulation
|
