CSCI 171 Presentation 15 Introduction to Object–Oriented Programming (OOP) in C++

Classes Templates from which programmatic building blocks are constructed –Extension of structures –Model physical entities –Programmer can ‘construct’ instances of the templates Instantiation Class contains: –Attributes (variables) –Behaviors (methods)

Example Write up the attributes and behaviors of a Car class

Objects Actual instance of a class In an object-oriented program objects interact with each other Objects may be constructed from other objects Black box concept –Other objects don’t care how an object performs its tasks, only that it does perform them

Important OOP concepts Encapsulation –The instances of each class have complete control over the accessibility of their attributes and behaviors as defined by the class –Methods and variables act as a cohesive unit Inheritance –Classes can be related in a hierarchical fashion from general to specific Polymorphism –Some instances of classes have the ability to morph themselves into other (related) classes

Encapsulation Access specifiers –public, protected, private Generally speaking –methods are public –variables are private

Inheritance Defining classes from general to specific –Allows for code reuse –Classes lower in a hierarchy obtain all features of higher level classes –All features should be put as high in the hierarchy as possible Create a class hierarchy for all vehicle objects

Polymorphism Assume we have a hierarchy with Animal at the top, and Crocodile and Dog below –An instance of an animal can reference a Crocodile at one time, and a Dog at another –This instance may respond differently to different methods depending on what it is referencing

Identifying Classes Done in design phase –define, design, code, test, document Most difficult part of OOP –must view entire system in OO terms –good initial design leads to highly effective programming –bad initial design leads to wasted time and effort

OOP in C++ Classes consist of 2 parts –Header all data and method signatures, and all corresponding access specification –Body method bodies

OOP in C++ Memory allocation – creating instances –Constructor method Same name as class If a pointer is used – dynamic memory allocation is done automatically using the keyword ‘new’ If non-pointer – static memory allocation is done –Destructor method Same name as class preceded by ~ If a pointer is used –memory is freed using the keyword ‘delete’ If non-pointer – destructor must be called explicitly