Object-oriented
programming (OOP) is a technique for writing computer software. The term
object oriented refers to the methodology of developing software in which the emphasis is
on the data, while the procedure or program flow is de-emphasized. That is, when designing
an OOP program, you do not concentrate on the order of the steps that the program
performs. Instead, you concentrate on the data in the program and on the operations
that you perform on that data.
Advocates of object-oriented programming claim that applications that are developed
using an object-oriented
approach
-
are easier to understand because the underlying code maps directly to real-world concepts
that they seek to
model
-
are easier to modify and maintain
because changes tend to involve individual objects and not the entire
system
-
promote software reuse because
of modular design and low interdependence among modules
-
offer improved quality because
they are constructed from stable intermediate classes
-
provide better scalability for
creating large, complex systems
Object-oriented application design determines
which operations are performed on
which data, and then groups the related data and operations into categories. When
the design is implemented, these categories are called classes. A
class defines the data and the operations that you can perform on the data. In
SAS/AF software, the data for a class is defined through the class's attributes, events,
event handlers, and interfaces. (Legacy classes store data in
instance variables.) The operations that you perform on the data are called methods in
SAS/AF software.
Objects are
data elements in your application that perform some function for you.
Objects can be visual objects that you place on the frame—for
example, icons, push buttons, or radio boxes. Visual objects are called
controls; they display information or accept user input.
Objects can also be nonvisual objects that manage the application behind the scenes;
for example, an object that enables you to interact with SAS data sets may not have
a visual representation
but still provides you with the functionality to perform actions on a
SAS data set such as accessing variables, adding data, or deleting data. An object or
component is derived from, or is an instance of, a class. The terms object, component, and
instance are interchangeable.
Software objects are
self-contained entities that possess three basic characteristics:
a collection of attributes and their current values. Two of a Push Button
control's attributes are
label (the text displayed on the
command push button) and
commandOnClick (the
command that executes when the command push button is pressed). You
can set these values through the
Properties window or through
SCL.
behavior
a collection of operations that an object can perform on itself or on other objects.
Methods define the operations that an
object can perform. For example, a Push Button can set its own border style via the
_setBorderStyle
method.
identity
a unique value that distinguishes one object from another. In SAS/AF, this identifier is referred to as its object identifier. The object identifier is
also used as the first-level qualifier in SCL dot notation.
This chapter describes how object-oriented techniques and related concepts are implemented
in
SAS Component Language (SCL) and in
SAS/AF software.