Page 225 - DCAP408_WEB_PROGRAMMING

Unit 9: ASP Objects

Let’s look at each of these aspects in turn: Notes

How It Works
The three categories that we have created in the left-hand column can be applied to any object.
In fact, the best way to describe an object is to break down its characteristics into these three
categories, and put information about your object into these categories. Any information that
you have about a particular object can be included in one of these categories.

If you have another telephone that features all these characteristics, except that its color is blue,
then we can describe your telephone by changing that one part of the description above. Moreover,
this technique works for any type of object, both real world and software.
9.1.1 The Building Blocks of Objects (Properties, Methods, Instances of
Objects)

Object Terms

So far, we have used verbose English terms to describe our three categories. In the world of
objects, we need terms that concisely describe each of these three categories. These terms are
properties, methods and events. In addition to these terms, we need to look at the term instance
as it relates to objects. In this section, we’ll look more carefully at what each of these means in
abstract terms.

Instances and Classes

When we are talking about a unique object, we can use the term instance to say that we are talking
about a particular telephone object - your telephone for example - that has a specific set of properties
and values. When we want to talk about another telephone, we use a different instance of the
telephone object. In this way, both you and we can have instances of the telephone object.
For example, my telephone (my instance of a telephone object) is gray and comes with special
answer-phone facilities, your telephone (your instance of a telephone object) may be red, blue,
green, etc. These instances represent completely different physical objects. However, since they
are both instances of the same object description or template, they share the same types of
characteristics such as methods, properties (although the values can be different), and events.
When a specific instance of an object is created from the template for the object, the object is said to
have been instantiated. What actually happens is that a copy is made of all of the properties and
events from the object description, but the methods (frequently a big chunk of code) remain in the
original place and this section of code is used by all of the different instantiations of that one object.

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