Classes

1. Classes

2. Object-Oriented Design • Method for designing computer programs • Consider “objects” interacting in the program • Example: a zoo, a gradebook

3. OOD Goals • Robustness • Gracefully handle failures • Adaptability • Evolve as necessary • Reusability • Many programs use same piece of code

4. OOD Principles • Abstraction • Abstract Data Types (ADTs) • Interfaces • Encapsulation • Information Hiding • Modularity • Easily plug together components

5. What is a class? • Data and the functions (methods) that operate on that data – collectively called members • Example: bank account class • Provide structure for organizing programs • Almost like an advanced struct

6. Syntax class classname { private: … public: … } • private only accessible within the class • public accessible from anywhere (like with a struct)

7. Member Functions • Typically, data (variables) declared private • Functions operate on data • accessor functions – read data, provide access to data but do not change it • update functions – change data • examples from bank account, zoo??? • constructor – builds a new object

8. Writing Classes • Typically, two files header and source • Header declares member variables, provides function prototypes and bodies of short functions • Source provides code for rest of functions • Allows separation of interface and implementation • Reduces compile time

9. Bank Account Interface • BankAccount(double initial_balance); • void withdraw(double amount); • void deposit(double amount); • double checkBalance() const;

10. Creating and Using Objects BankAccount b(500); //Type Name(constructor parameters); //how would you withdraw funds?

11. Creating and Using Objects BankAccount b(500); Type Name(constructor parameters); //how would you withdraw funds? b.withdraw(300); object_name.method_name(param list);

12. Constructor BankAccount::BankAccount(double init_balance) class_name(parameter list) • Special-case function called when a new object is created • Used to initialize member variables • Examples? • Default constructor takes no parameters

13. Alternative Initialization BankAccount::BankAccount(double init_balance) { balance = init_balance; } BankAccount::BankAccount(double init_balance=0) : balance(init_balance) { }

14. Destructor BankAccount::~BankAccount() ~class_name • Used if class allocates memory dynamically (uses new) • Delete all dynamically declared objects

15. const • const member function will not change any class variables • double checkBalance() const {…}

16. friend • Allow a class to access the private members of another class • Operator overloading • Closely related classes

17. static • Static class member - a global variable with scope the same as a class member • 1 per class, not per object • Example - car serial number

18. More Examples • An appointment book/calendar • A tic tac toe game • Airline example