Object Oriented Programming A brief review of what you should know about OOP

Programming Paradigms What is a paradigm? –A model, pattern, or typical example –A world-view used in doing something What are programming paradigms? –Virtual computer models for writing code Examples of programming paradigms –Machine code, assembly language –Structured programming; OOP

Structured programming Early paradigms focused on the hardware –This approach focused on execution sequence, program flow –Many programmers wrote “spaghetti” code In 1968, Edgar Dijkstra published a letter: –GOTO considered harmful –Structured logic more readable: If-then-else, while-loops, single-entry/exit blocks

The OO Paradigm In 1976, Niklaus Wirth (neeklouse veert) Algorithms+Data Structures = Programs Don’t focus on just algorithms (code flow) Balance data & algorithm emphasis at every level of programming Use modules that include data structure and operations

OOP objects OOP is based on objects that have data and operations (methods) The data describes the object’s –State, and –Properties The methods describe –What you can do to the object, and –What you can have it do for you

Prototype and Instance Objects Most OO models allow dealing with objects in two ways: –Prototype objects are models for lots of similar objects: car, person, pet, package –Instance objects are specific examples: my 1996 red Civic, Jay Leno, Sarah’s puppy, my Christmas gift from my son Eric In some languages, prototype objects are called classes and/or types

Object interaction Objects interact with each other using –Messages! –In some languages, messages are implemented by function calls –When you click on an object to get a context menu and then select a choice from the menu, you are “sending it a message” to perform that method (operation) –It may cause a return message (return value)

Features of OOP Programming languages that support OOP provide 3 features: –Encapsulation –Polymorphism –Inheritance

Encapsulation Encapsulation is the OOP feature that provides container modularity 2 ways - –Grouping: allowing related data and a set of operations to be grouped (remember Wirth?) –Hiding: protecting the internal workings of the “black box” and defining the external interface or how you can interact with the box

Polymorphism Polymorphism is language support for using the same name for similar operations on different kinds of objects It would be very disappointing to need to learn separate names or operators for adding ints, floats, and doubles instead of just using “+” for each of them

Polymorphism in C++ Polymorphism is provided in C++ by –Automatic type conversions –Function & operator overloading –Inheritance Member function overriding Virtual functions and pure virtual functions –Templates –+ overload resolution is involved in all of these We will use each of them in this class!

Inheritance In OOP, inheritance is a form of “factoring” An expression can be easier to calculate if you separate out a common factor If a program uses the same code several places, “factor” it out as a function to call If a bunch of objects have shared subsets of data and operations, “factor” out a base class (and only maintain it one place)

Inheritance and Sub-classes The usual reason why objects share data properties and operations is sub-classing Cars, trucks, busses, boats, and airplanes share many properties and operations because they are all vehicle sub-classes Students, faculty, and staff share object properties and operations because they are all people

C++ Features to Review Here are some OOP features of C++ –Public, private, and protected in classes –Defining classes using inheritance –Visibility rules in derived classes (inheritance) –Function overloading Operator overloading (including I/O: >) Differences for member functions You should review all of these!