Object Oriented Programming

1. Object Oriented Programming It Puts the ++ in C++

2. Why O-O? • It makes data the main focus • Objects translate from real-world objects • Allows for abstraction (Too many details!) • Allows for encapsulation for security and reuse • Promotes modularity • Design, develop and test classes independently • Promotes reuse (did I mention reuse?) • Project management • Memory management • Stack vs. heap control over allocation and deallocation of memory • Dynamic vs. static

3. The Header of the Class • The class structure is the blueprint for future objects • Class components are allowed to be private • Mostly for protecting data • Data can only be shared through a public function that YOU (the programmer) will control • Class components are allowed to be public • Mostly for sharing functions. • Member function prototypes listed here • Can be accessed (called) directly from a client’s function • main() • Other non-member function

4. The Header of the Class • Class structure is an interface • Provides a list of member functions without revealing details • Provides parameters of each function and correct usage • Info for client about what is available • The class file is called the header file • Filename ends in .h

5. Class Structure

6. Class Interface • Reveals what client can use in class and how • Reveals to implementer what it needs to work • Lists data and operations • Data members (fields) • Member functions (methods) • Use public/private sections to control access to clients

7. Preconditions and Postconditions • Communicates what a function accomplishes without indicating how it accomplishes it • Contract between two programmers • Client programmer • Implementation programmer • Precondition statement indicates what must be true before a function is called • Required state or range of data being passed to the function • Postcondition statement indicates what will be true when the function finishes its work • What to expect from the function

8. Access to Data Members • Members declared on stack, but can also be declared in heap • Client can access public features only—error returned for calls to private members • Member functions can access private data members and return to client • Accessor method: method that returns or displays private data • Control over data formatting • Control over which data is accessible and in which state • Mutator method • Controls how data is modified • Controls where data is saved • Can constrain changes to a specified range • Can enforce business rules for data

9. Implementation • Contains complete member function code • Kept in separate .cpp file in IDE project folder • Must include #include “class.h” • System header file in default location #include <assert> • Client header file in current (IDE project) directory • Preprocessor replaces #include line with entire contents of the file • Function name gets class name identifier for class level scope • Class::functionName • Otherwise function is non-member function (global scope)

10. Class Structure

11. Interface and Implementation Separate • Separate physical files for interface and implementation • Must keep them in sync; change to any part of prototype must be changed in both files

12. Accessing Private Data in Public Functions • All data members are accessible directly within a member function • No object needed • Dot notation not necessary • Can call other member functions (both public and private) from within a member function

13. Class Constructor • Constructor • Member function that initializes all data member functions to a valid state • You must write it--not automatically set to default • Unique Prototype • No return type • Exactly same name as class • Can have parameters, but if provided the client must use them • Can be overloaded to provide client more than one option for parameters • Otherwise, just like other member functions • Must be included in class definition and implementation file • Must have class:: keyword in implementation

14. Destructor • Function to clean up after an object is destroyed • Called automatically on delete call or when leaving object scope • Unlike the constructor, you don’t always need a destructor • Can use it to remove very large objects from memory if memory is an issue • Unique prototype • Exactly same name as class, but prefixed with ~ (you’ll find this symbol above the tab on most keyboards) • No parameters • No return type

15. Client Program • Client uses class as an abstraction • Invokes public operations only • Internal implementation not visible • Client can’t and shouldn’t change internals • Class data should be private • Interface is used by the client programmer to use the class • Get information to use objects of that class, without having to manage functionality associated with it.

16. Data Storage • Client program will declare object on stack • Each data member defined in the class is associated with that object declaration • Client program can declare many objects on stack of same class • Each object has its own copy of each data member defined in that class • If a client program accesses data for an object, it is accessing the data for that copy of the member data for that class only.

17. Driver • Client program could be a lot like a driver. • Create objects of classes to be used • Call functions of those objects • Call non-member client functions • To handle specific tasks of client • Otherwise, may have no original code • master controller program

18. Client Structure Uses #include <libraries> Uses #include “class.h” Can have using namespace std; Client file has .cpp extension

19. Class Structure

20. How to Use Objects Private Member Variables – How To Access Them… Public Member Functions

21. Non-Member Functions • Non-member functions: • Not part of a class • Not part of a client • Can be implemented in either • Class implementation file • Client file • Global scope • Does not have access to private class data • Has access to public class functions (must use an object)

22. Helper Function • Private member function of a class • Cannot be called by a client or non-member function (with or without an object)—it’s private! • Can be called by another member function of the same class only • Needed to help one or more public member function of the same class • Can be used to provide private data manipulation needed as a precondition of a member function

23. Friend Function Non-member function with access to private class data Prototype in class header—public or private Includes friend keyword in prototype in header file only Implemented in implementation .cpp file without the class:: keyword Because it is a non-member function, the client calls this function without an object: function ( ) not object.function( ) Friend function can access private data, but not directly—must use an object of the class and dot operator: object.variable

24. How To Use Functions Interface Prototype Implementation Declaration

25. How To Use Functions Client

26. Operator Overloading • Syntax convenience • Way of allowing more than one way to use the class as an object • Client can create object and provide data to set the intial state of member variables OR • Client can create object without providing data (contructor will set intial state) • Way of using common operators for objects • Example: + vs function called add

27. Overloaded Operator Precedence • To overload for an operator, implement function named operatorX (Where X represents the operator you are interested in) • For a class member function, the left hand side of the equation is the receiver object and other operands are passed as arguments • f1 + f2 • sum = f1.operator+(f2) • For a non-member function, two operands are on equal footing • f1 + f2 • sum=operator+(f1, f2)