13:25:00
Aggregation
& Encapsulation
This is also called as composition model. Example in
order to make a “Accounts” class it has use other objects example “Voucher”,
“Journal” and “Cash” objects. Therefore, accounts class is aggregation of these
three objects.
It's has a
relation with one owner (Association and aggregation are almost same with just
one difference, in aggregation we have one owner but in association there
is no owner)
Manager has N Employees for a
project. Team has Players.An aggregation is used when life of object is
independent of container object But still container object owns the aggregated
object.
E.g. Team has players, if team dissolve, Player will still exists.
Life
or existence of the aggregated objects are
independent of each other, But one object is playing the role of Owner of the
other object.
Composition
It's has a relation but it's a specialized form of
Aggregation
Composition is a special case of aggregation. In a
more specific manner, a restricted aggregation is called composition. When an
object contains the other object, if the contained object cannot exist without
the existence of container object, then it is called composition.
Class
A contains Class B
- Order consists
of Line Items.
- Body consists of
Arm, Head, and Legs.
- Bank Account
consists of Balance and Transaction History.
·
A
composition is used
where each part may belong to only one whole at a time.
·
E.g. A line item is part of an order so a line item cannot exist without an order.
Life or existence of the composite object is
dependent on the existence of container object, Existence of composite object
is not meaningful without its container object.
.
Encapsulation
It is a process
of hiding all the internal details of an object from the outside world.
Encapsulation is another pillar of Object Oriented programming.
Object should hide its inner working from outside world. Keeping member
variables as private and restricting it from exposing to outside world helps
objects to avoid unwanted changes to variables. Functionalities of the object
is available to outside world thought its public methods only.
The wrapping up
of data and its functions into a single unit is called Encapsulation.
When using Data
Encapsulation, data is not accessed directly, it is only accessible through
the functions present inside the class.
You experience encapsulation in your daily life all
the time. Think about a human resources department. They encapsulate (hide) the
information about employees. They determine how this data can be used and
manipulated any request for the employee data or request to update the data has
to be routed through them. Another examples network security. Any request for
security information or a change to a security policy must be made through
a network security administrator. The security data is encapsulated from the
users of the network.
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