Page 226 - DCAP408_WEB_PROGRAMMING

Web Programming

Notes So we’ve mentioned object descriptions or templates, but it’s time to give them their proper
name in ASP; classes. We mentioned that each object can have different instances. For instance,
my telephone is small and white and has 12 buttons. Your telephone will probably be different
to that, but they’re both recognizable as telephones and they both provide the same function.
They both conform to a set of rules for what a telephone does - they connect to the local
telephone line, they both have a numeric keypad and somewhere to speak into. A class in ASP
is like a set of design rules that an object must conform to. It would be no good if my telephone
didn’t have a handset, or a numeric keypad, even if it did plug into the telephone socket on the
wall.

!
Caution In a class there should be a minimum set of functions that your object must be able
to perform.

Properties

When talking about those characteristics that describe an object, we are talking about the properties
of the object. Each property of the object describes a particular aspect of the object. The property
is actually described as a name/value pair. This means that for every named property, there is
a single unique value that describes that property for this instance of the object. If we go back to
our telephone example, we can create a table that lists each of the property names and the value
of each property.

We now have a set of properties that describe this instance. The properties of an object are used
to represent a set of values associated with the object. A new instance of the object may have
different property values, but it has the same property names.

Even with different property values, these two telephones are instances of the same object
template. Since we know that all telephone objects have a ‘Color’ property, we can determine
the color of each of the phones by examining its ‘Color’ property value. We can use properties
in two ways. We can read from them or we can also write to them. So if we wanted, we could
have changed the cover of our telephone to a different color, if we required.

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