Chapter 2 Objects and Classes

1. Chapter 2Objects and Classes Saurav Karmakar Spring 2007

2. 2.1 What is OO programming? • Object: an atomic unit that has structure and state • Information hiding: Black-box analogy • Encapsulation: grouping of data and functions • Inheritance: mechanism allows extending functionality of an object.

3. How does C++ support OO • Template: the logic is independent of the type • Inheritance • Polymorphism: can hold different types of objects. When operations are applied to the polymorphic type, the operation appropriate to the actual stored type is automatically selected.

4. 2.2 Basic Class Syntax • Class members: either data or functions and categorized into either public, protected,or private. • Public: visible to all routines and may be accessed by any methods in any class. • Private: not visible to nonclass routines and are accessed only by methods in its class. • Protected: similar to private but visible to derived classes. • Default: all members are private

5. Constructors • Member functions/methods that describe how an object is declared and initialized. • If no constructor defined, compilers will generate one called default constructor. • Explicit constructors prevent automatic type conversion.

6. Constant Member Function • Mutators change the state of the object but accessors are those who don’t. • Constant member function: functions that do not change any class data member. • const is a part of the function signature. [const] return_type name([const] parameter_list) [const];

7. Interface & Implementation • Interface lists the class and its members and describes what can be done with the object. • Implementation represents the internal process by which the interface specifications are met. • Scope operator use : Systax : Classname ::member • Signatures must match exactly.

9. TestIntCell.cpp • #include <iostream.h> • #include "IntCell.h" • int main( ) • { • IntCell m; // Or, IntCell m( 0 ); but not IntCell m( ); • m.write( 5 ); • cout << "Cell contents: " << m.read( ) << endl; • return 0; • }

10. Big three: Destructor, Copy Constructor, and Operator = •Destructor tells how an object is destroyed and frees the allocated resources when it exists scope. ~IntCell(); •Copy Constructor allows a new object construction using the data in from existing one. IntCell a = b; // a new IntCellcall a IntCell a( b ); // a new IntCellcall a •Operator = copy assignment, copies data members using = by default. => may cause shallow copying.

11. This (predefine pointer)

12. 2.3 Additional C++ Features • Operator overloading: extending the types to which an operator can be applied. example: string x=“Mary’s score is:”; int y=95; string z=x+y; • “.”, “.*”, “?:”, “sizeof” can’t be overloaded

13. Additional C++ Features • Type conversion creates a temporary object of a new type– Example: int a = 5; double b = a; //implicit cast

14. 2.5 Exceptions (report error) • An object that stores information transmitted outside the normal return sequence and is used to signal exceptional occurrences. • Handle exceptions by throw and catch clauses.

15. Exceptions example try { for (int n=0; n<10; n++) { if (n>9) throw "Out of range"; } } catch (char * str) { cout<< "Exception: " << str<< endl; }

16. 2.6 String Class • C string: array of character terminated by ‘\0’ • C++ standard string: a STL class with all overload operators and built-in functions • http://www.bgsu.edu/departments/compsci/docs/string.html

17. Array size extension • int *original =arr; arr = new int [12]; for(i=0; i<10; i++) arr[i] =original[i]; delete [] original;

18. Summary • Construction/ destruction of objects • Copy semantics • Overloading • Implicit/explicit type conversion • Information hiding/atomicity