Inheritance

• There are three types of relationships b/w objects

  • association
  • composition
  • aggregation

• There is one more kind of relationship b/w objects which can be referred as is a relationship. This is a relationship is formed by inheritance

• Refer Here for the UML Diagrams

• Consider a Rental Vehicle Application

• Code Example

class Vehicle:
    def start_hire(self):
        print("hire started")

    def stop_hire(self):
        print("hire finished.")

class Bike(Vehicle):
    pass

vehicle = Vehicle()
vehicle.start_hire()
vehicle.stop_hire()

pulsar_bike = Bike()
pulsar_bike.start_hire()
pulsar_bike.stop_hire()

• Chess Pieces

• Lets try to design classes for Chess Game

  • Player
  • Chess Set
  • Pieces
    • Pawn
    • Rook
    • Knight
    • Bishop
    • Queen
    • King
  • Board
  • Position (64 Positions)

• Pieces Class Diagram

• Complete Class Diagram

• Sample code for the classes

class Piece:
    """
    This represents a piece in the chess game
    """
    def __init__(self,color,board): 
        """
        Initializer for the piece
        """
        self._color = color
        self._board = board

    def move(self):
        """
        This method defines the movement of chess piece
        """
        print("No movement defined")


class Pawn(Piece):
    def move(self):
        print("Single positon forward or cross")

class Bishop(Piece):
    def move(self):
        print("Move Cross in any direction by any number of steps")


class Board:
    pass
my_chess_board = Board()

bb1 = Bishop(color='Black', board=my_chess_board)
bb2 = Bishop(color='Black', board=my_chess_board)
wb1 = Bishop(color='White', board=my_chess_board)
wb2 = Bishop(color='White', board=my_chess_board)
bb1.move()

bp1 = Pawn(color='Black', board=my_chess_board)
bp1.move()

Exercise

• Create a Class Diagram for Bus Ticket Booking application
• Here the following are the few classes
  • User
  • Bus
    • Sleeper
    • Seater
    • Sleeper and Seater
  • Bus Agency
  • Ticket
  • Route