The below post explains Object and
Class
What
is an Object?
An object represents an entity, either physical, conceptual or
software.
Ø Physical
– Car or a Person
Ø Conceptual
– Chemical Process
Ø Software
– Bill Number 101, Purchase Order SO01
An object is an entity with
a well-defined boundary and identity that encapsulates its state & behaviour:
Ø Identity
- a name
Ø State
- determined by the values of its attributes
Ø Behaviour
- determined by how the object acts or reacts to requests (messages) from other
objects
Object
Has State
The state of an object is
one of the possible conditions in which an object may exist
The state of an object
normally changes over time
E.g. Rahul is an object of class Employee. The Rahul
object has state:
-
Name= Rahul
-
Employee Id=123
-
Hire date=02/02/2013
Object
has Behaviour
Behaviour determines how an object acts and reacts to requests from other objects.
The visible behaviour of an
object is modelled by the set of messages it can respond to (operations the
object can perform)
Employee Rahul’s Behaviour:
-
Submit TimeSheet()
-
Complete TaskAssigned()
The behaviour may change
the state of an object.
Object
has Identity
Each object has a unique
identity, even if the state is identical to that of another object.
E.g. Employee Rahul is from
XX City. Even if there is another employee with the same name – Rahul working
in same city or another city they both are distinct objects
What
is a Class?
A class is a description of
a set of objects that share the same attributes, operations, relationships and
semantics.
Ø An
object is an instance of class
A class is an abstraction
in that it
Ø Emphasizes
relevant characteristics
Ø Suppresses
other characteristics
Relationship
between Classes & Objects
Ø A
class is an abstract definition of an object.
Ø It
defines the structure & behaviour of each object in the class
Ø It
serves as a template / blue print for creating objects
Attributes
of a Class
Ø An
attribute is a named property of a class that describes a range of values that
instances of the property may hold
Ø A
class may have any number of attributes or no attributes at all.
Ø An
attribute has a type, which tells us what kind of attribute it is.
Ø Typically
attributes are integer, boolean, varchar etc. These are called primitive types.
Ø Primitive
types can be specific for a certain programming language.
Operations
of a Class
Ø An
operation is the implementation of a service that can be requested from any
object of the class to affect behaviour
Ø A
class may have any number of operations or none at all
Ø The
operations in a class describe what class can do
Ø The
operation is described with a return-type, name, zero and more parameters. This
is known as signature of an operation
Often,
but not always, invoking an operation on an object changes the object’s data or
state Original Post At : http://learnerpoint.in/2017/01/02/understanding-object-and-class/