1. Object-Oriented Design

2. Method for designing computer programs Consider “objects” interacting in the program –Example: a zoo

3. OOD Goals Robustness –Gracefully handle failures Adaptability –Evolve as necessary Reusability –Many programs use same piece of code

4. OOD Principles Abstraction –Abstract Data Types (ADTs) –Interfaces Encapsulation –Information Hiding Modularity –Easily plug together components

5. Inheritance Many objects have a hierarchical relationship –Examples: zoo Inheritance allows software design to take advantage of relationships

6. Terminology Base class/Parent class/Superclass –defines generic functionality Derived class/Child class/Subclass –extends or specializes base class –inherits members of parent –may implement new members –may override members of parent

7. Examples Card Game Airline Reservation System

8. Syntax class Student : public Person {…} class Derived : public Base{…} Derived class may override or reimplement a function implemented by base class class Person {class Student:public Person{ … void print(); }

9. Function Invocation Person – print, getName Student – print, changeMajor Person p(…); Student s(…); s.getName(); p.print(); s.print(); p.changeMajor(); s.changeMajor();

10. Function Invocation Person – print, getName Student – print, changeMajor Person p(…); Student s(…); s.getName(); //Person::getName p.print(); //Person::print s.print(); //Student::print p.changeMajor(); //ERROR!!!!!!!! s.changeMajor(); //Student::changeMajor

11. More Syntax void Person::print() {…} void Student::print() { Person::print(); //Superclass::function(); … }

12. Protected private members of parent not accessible to child class protected members accessible only to derived classes examples class classname { private: protected: public: }

13. Child Class Constructors Subclass must create superclass –invoke superclass constructor from subclass constructor –use initializer list Student::Student(string newname, string newmajor) :Person(newname), major(newmajor) {…} Student::Student(string newname, string newmajor) :Person(newname) {major = newmajor;}

14. Static Binding Person* p = new Person(…); Student* s = new Student(…); p->print(); //calls Person::print() p = s; //OKAY p->print(); //calls Person::print() p->changeMajor(); //ERROR Function called depends on declared type

15. Dynamic Binding May want to determine which function to call based on object contents Use virtual functions class Person { virtual void print(); } class Student : public Person { virtual void print(); }

16. Dyanmic Binding Person* p = new Person(…); Student* s = new Student(…); p->print(); //calls Person::print() p = s; //OKAY p->print(); //calls Student::print() p->changeMajor(); //ERROR

17. Polymorphism Many forms A variable is polymorphic if it points to an object with 1 or more virtual functions

18. Casting Person* p; p = new Student(…); Student* s = dynamic_cast (p); Create new pointer of subclass type to point to object Pointer (s in this case) will be NULL if cast was NOT successful Can also use C-style cast

19. Abstract Classes May want to defined base class which cannot be instantiated –Examples – bank account, car Declare one or more functions as pure virtual virtual void print() = 0; virtual void func_name(…) = 0;

20. Templates template class BasicVector {} BasicVector iv(5); BasicVector sv(100); Define classes which can hold any type of object

21. Exceptions If error occurs during runtime, report and continue execution –Example: array index, divide by 0 Exceptions are also classes –programmer defines try { //call func that throws exception } catch(ExceptionType& et) { //e.g., print error } catch(…) { //catch all exceptions } void func() throw(ExceptionType) {…}