Page 14 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Object Oriented Analysis and Design

Notes but inherit-mice and polymorphism add power. The ability to abstract is probably the most
important skill required for object oriented development.

1.3.2 Encapsulation

Encapsulation is the process of encapsulating the elements of an abstraction that constitutes its
structure and behavior; encapsulation serves to separate the contractual interface of an abstraction
and its implementation.
It can also be called as information hiding. It consists of separating the external aspects of an
object, which are accessible to other objects, from the internal implementation details of the
object, which are hidden from other objects. It is not unique to object oriented languages.
Encapsulation (also information hiding) consists of separating the external aspects of an object,
which are accessible to other objects, from the internal details of the object, which are hidden
from other objects.
Objects have an outside (how they are seen or interact) and an inside (what they are.)
Encapsulation means that every object is self-contained.

Encapsulation is not a unique concept to OO languages, but the ability to combine data and
behavior in an object provides cleaner encapsulations than with conventional languages.
Objects restrict the visibility of their resources (attributes and methods) to other users. Every
object has an interface, which determines how other objects can interact with it. The
implementation of the object is encapsulated, that is, invisible outside the object itself.
Separate the external aspects of an object (its interface) from the internal implementation details
(implementation).
Proper encapsulation keeps objects from becoming interdependent (or coupled) - internal details
can change with no affect on the user. Encapsulation places a premium on interfaces.

!
Caution Encapsulated details can change with no impact to a client, while an interface
change directly affects a client.

1.3.3 Combining Data and Behaviour

The caller of an operation need not consider how many implementations of a given operation
exist. Operator polymorphism shifts the burden of deciding what implementation to use from
the calling code to the class hierarchy.
As an example, let us talk about an object oriented program calling a draw procedure for
drawing different figures say a polygon, circle, or text. The decision of which procedure to use
is made by each object, based on its class.

1.3.4 Sharing

Inheritance of both data structure and behavior allows common structure to be shared among
several similar subclasses without redundancy. The sharing of code using inheritance is one of
the main advantages of object oriented languages.
One of the reasons for the popularity of object-oriented techniques is that they encourage sharing
at different levels. Inheritance of both data structure and behavior allows common structure
(base class) to be used in designing many subclasses based on basic characteristics of base class,

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