Std 12 computer chapter 6 object oriented concepts (part 2)

Object Oriented
Concept
Part 2
Aggregation & Composition
Aggregation vs. Composition
Inheritance
Composition vs. Inheritance Presented by Nuzhat Ibrahim Memon

Presented by Nuzhat Ibrahim Memon
2
Name
• first name: String
• last name: string
• display()
Person
• nm: Name
• addr:Address
• birthdate:date
• setbirthdate(d:int, m:int,
y:int):date
Address
•house: string
•street:string
•state:string
•pincode:int
•fulladress(): string
Teacher
• Subject : string
• lecture(d:date, t:time)

• When objects of one class are composed of objects of
other class, it is called aggregation or composition.
• It represents “has-a” or “a-part-of” relationship
between classes.
3
Person
• nm: Name
• addr: Address
• birthdate:date
• setbirthdate(d:int, m:int,
y:int):date
• display()
Name
• First Name: string
• Middle name:string
• last name:string
• fullName():string
• display()
Address
• house: string
• street:string
• state:string
• pincode:int
• fulladress(): string
• display()
Screen
• length: int
• width: int
• model: string
Motherboard
• model: string
• company: string
computer
• scr: Screen
• mb: Motherboard
• Take an example of ‘person’ class
• We will define two classed ‘Name’ and ‘Address’.
• Class ‘Name’ has an attribute first name, middle
name and last name.
• Class ‘address’ has an attribute house, street, city,
state and pincode.
• The data type of attributes ‘nm’ and ‘addr’ is class
‘Name’ and ‘Address’ respectively.
• Thus class ‘person’ contains object of class ‘Name’
and ‘Address’

• Aggregation represents non-exclusive relationship between two
classes.
• In aggregation, the class that forms part of the owner class can exist
independently.
• The life of an object of the part class is not determined by the owner
class.
• Object Address may be shared by more than one person. Address is
not exclusive to any one person. So, when a person is deleted, the
corresponding address cannot be deleted.
• Basic aggregation is represented using an empty diamond symbol
next to the whole class.
• Composition represents exclusive relationship between two classes.
• Composition is a strong type of aggregation where the lifetime of the
class depends on the existence of the owner class.
• If an object of aggregating class is deleted, its part class object also
will get deleted. For eg. When an object of class person is deleted, the
object of class name is also deleted. Name is associated exclusively
with single person.
• Composition relationships are represented using a filled diamond
next to the whole class.
Owner class,
Whole class or
aggregating class
4
Name
• first name: string
• Middle name: string
• last name: string
• display()
Person
• nm: Name
• addr:Address
• birthdate:date
• setbirthdate(d:int,
m:int, y:int):date
Address
•house: string
•street:string
•state:string
•pincode:int
•fulladress(): string
Subject class,
part class or
aggregated class
Subject class,
part class or
aggregated class
Composition Relationship
(Filled diamond)
Aggregation Relationship
(Empty diamond)

• Inheritance is generally referred to as ‘is-a-kind-of’ relationship
between two classes.
• Inheritance is appropriate when one class is ‘a kind of’ other
class. For e.g. teacher is a kind of person. So, all the attributes
and methods of class ‘Person’ are applicable to class ‘Teacher’
also.
• Inheritance refers to the capability of defining a new class of
objects that inherits the characteristic of another existing class.
• In other words, class ‘Teacher’ inherits all attributes and
behavior of class ‘Person’. Class ‘Teacher’ may have additional
attributes like subject and method like taking lectures of the
subject. In such scenario, class ‘Teacher’ can be defined using
class ‘Person’.
• The feature provides reusability where existing methods can be
reused without redefining. In other words, the data attributes
and methods of the super class are available to objects in the
sub class without rewriting their declarations.
5
Person
• name:string
• city: string
• gender:char=‘F’
• setBirthdate(d:int, m:int, y:int):date
• display()
Teacher
• subject: string
• lecture (d:date, t:time)
Existing class is called New Class is called
super class sub class
parent class child class
base class derived class
In Class Diagram, Inheritance is represented using
an arrow pointing to super class.

6
• Generalization is another name for inheritance or “is a” relationship.
• It refers to a relationship between two classes where one class is a specialized
version of another.
• Common attributes and methods are defined in super class.
• Sub class is a specialized version with additional attributes and methods.
• There may be a classical hierarchy of inheritance between classes. For e.g. class
‘Employee’ can be derived from class ‘Person’, then class ‘Teacher’ can be derived
from ‘Employee’. Here employee is a kind of person and teacher is a kind of
employee. Such type of inheritance is known as multilevel inheritance.
• A class can also be derived using more than parent classes. For e.g. a child inherits
the characteristics of both mother and father. When a class is derived from two or
more classes. It is known as multiple inheritance. In multiple inheritance, child will
get properties from father as well as mother from both the parents.
• Example: airplane is a kind of vehicle as well as flying object.
Person
Teacher
Employee
Child
Father Mother
Airplane
Vehicle
Flying
object
Person
(Super Class)
Teacher
(Sub Class)
Common attributes & methods
Additional attributes & methods
Grandfather
Son
Father

• In inheritance, class inherits from other classes
in order to share, reuse or extend functionality.
Here there exists ‘is a’ or ‘a kind of’ relationship
between super class and sub class.
• In composition, classes do not inherit from other
classes, but are ‘composed of’ other classes.
Class contains the attributes where some
attributes are of objects of other class types.
7
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Nuzhat Memon
website:
nuzhatmemon.com
Email:
nuzhat.memon@gmail.com

Std 12 computer chapter 6 object oriented concepts (part 2)

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Std 12 computer chapter 6 object oriented concepts (part 2)