Transcript Object Oriented Programming

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: << and >>)
• Differences for member functions
• You should review all of these!