Object Oriented Design and Classes

What is a class? Programming mechanism to support OOD Data and the methods that operate on that data – collectively called members –Example: bank account class Provide structure for organizing programs

Methods Methods operate on data –accessors – read data, provide access to data but do not change it –mutators – change data examples from bank account, zoo –constructor – builds a new object An object in an instance of a class –class is a blueprint for objects

BankAccount Class class BankAccount: def __init__(self, initial_balance): self.balance = initial_balance def deposit(self, amount): self.balance += amount def withdraw(self, amount): self.balance -= amount def checkBalance(self): print "Balance: ", self.balance

BankAccount Class def __init__(self, initial_balance): self.balance = initial_balance __init__ method is the constructor Used to initialize members of the object First parameter is self – the object on which the method/constructor is called Use dot notation (.) to reference members of the object

BankAccount Class def deposit(self, amount): self.balance += amount def withdraw(self, amount): self.balance -= amount Deposit and withdraw are mutators –they modify the data member balance First parameter is self Like functions, methods can take any number of parameters

BankAccount Class def checkBalance(self): print "Balance: ", self.balance checkBalance does not modify data members

Creating and Using Objects b = BankAccount(500) //Name = Type(constructor parameters)

Creating and Using Objects b = BankAccount(500) //Name = Type(constructor parameters) //how would you withdraw funds? b.withdraw(500) //object_name.method_name(params)

Composing Objects An object can have a reference to another object class Name: def __init__(self, first, last): self.first = first self.last = last def printName(self): print "Name: ", self.first, " ", self.last class Employee: def __init__(self, first, last, pay): self.name = Name(first, last) self.pay = pay def printEmployee(self): self.name.printName() print "\tPay rate: ", self.pay