Name: Design Patterns
Uploaded: 2021-12-27
Duration: 1 min 29 s
Description: . . Design Patterns used in the project - Group 7 - 33KDP.

. . Design Patterns used in the project - Group 7 - 33KDP. 

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Design Patterns used in the project - Group 7 - 33KDP

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Singleton
Used In - DBConn
We use the singleton design pattern to ensure that only one DBConn object is created to have a PDO
object to maintain the connection to the database within the whole application. When the PDO is
needed, we use the getInstance() static method of the DBConn class to get an object of the DBConn
class to access the PDO attribute of it. The constructor of the DBConn class is made private to ensure
that no other classes create objects without going through the getInstance method.

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Multiton
Used In - Tutor, Timeslot, Subject, Student
In most cases where these classes and their objects are used, we know the unique id, such as user_id,
tutor_id, student_id, or timeslot_id. In each of these classes, we maintain a list of instances as a
key-object pair for all the instances that were created previously. When an object of the relevant class is
needed we pass the id to the getInstance static method, we check if the object corresponding to that id
is present, and if it is, we return the object, and if not, we create the object using the private constructor
and add it to the instances list and return the object. This way we can ensure that only one object is
created for each id.

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State
Used In - Message, Request
Both Message and Request objects change their behavior at run time depending on their internal
states. Therefore, the State design pattern is used to alter their behavior and it acts as an
object-oriented state machine.
Message class has two concrete states(Read and Unread) which extend abstract class MessageState
and Request class has three concrete states(Pending, Accepted, Rejected) which extend the abstract
class RequestState.

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Template
Used in - _Class, Request, User
_Class, Request, and User classes act as templates for their concrete subclasses(_class →
IndividualClass, GroupClass, Request → EnrollRequest, JoinGroupRequest, User → Student, Tutor).
Methods in those abstract classes are overridden by the concrete subclasses and those subclasses
provide concrete behavior specific for each subclass.

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Proxy
Used in - StudentGroup
We use the Proxy method When displaying student group details. When we display student group
details we don’t need all the details of the group. Therefore, We need to control access to the original
student group object, allowing users to see only necessary details of the student group before the
request gets through to the original student group object. The original student group object is heavy so
we decided to use the proxy method here.

Design Patterns

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