Transcript Data Structures - Mount Holyoke College

Classes
Object-Oriented Design
• Method for designing computer programs
• Consider “objects” interacting in the
program
– Example: a zoo, a gradebook
OOD Goals
•
Robustness
– Gracefully handle failures
•
Adaptability
– Evolve as necessary
•
Reusability
– Many programs use same piece of code
OOD Principles
• Abstraction
– Abstract Data Types (ADTs)
– Interfaces
• Encapsulation
– Information Hiding
• Modularity
– Easily plug together components
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
Syntax
class classname {
private:
…
public:
…
}
• private only accessible within the class
• public accessible from anywhere (like with a
struct)
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
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
Bank Account Interface
• BankAccount(double initial_balance);
• void withdraw(double amount);
• void deposit(double amount);
• double checkBalance() const;
Creating and Using Objects
BankAccount b(500);
//Type Name(constructor parameters);
//how would you withdraw funds?
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);
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
Alternative Initialization
BankAccount::BankAccount(double init_balance) {
balance = init_balance;
}
BankAccount::BankAccount(double init_balance=0) :
balance(init_balance) { }
Destructor
BankAccount::~BankAccount()
~class_name
• Used if class allocates memory
dynamically (uses new)
• Delete all dynamically declared objects
const
• const member function will not change any
class variables
• double checkBalance() const {…}
friend
• Allow a class to access the private
members of another class
• Operator overloading
• Closely related classes
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
More Examples
• An appointment book/calendar
• A tic tac toe game
• Airline example