1. Introduction to Data Structures, Spring 2007 Slide- 1 California State University, Fresno Introduction to Data Structure Object Oriented Programming Concepts Ming Li Department of Computer Science California State University, Fresno Fall 2006

2. Introduction to Data Structures, Spring 2007 Slide- 2 California State University, Fresno Main Concepts of OO Programming Encapsulation –abstraction, information hiding Inheritance –code reuse, specialization Polymorphism –allows old code to use new code –The actual implementation of the called function depends on type of object

3. Introduction to Data Structures, Spring 2007 Slide- 3 California State University, Fresno Object Oriented Programming Encapsulation Hiding information within one abstraction Achieved via classes and objects.

4. Introduction to Data Structures, Spring 2007 Slide- 4 California State University, Fresno Object Oriented Programming - Inheritance New code using old code –Code reuse –Less development time –Better code quality Example –Table is the original class –DinningTable and ComputerTable can reuse the code of Table class

5. Introduction to Data Structures, Spring 2007 Slide- 5 California State University, Fresno Object Oriented Programming - Polymorphism Old code using new code. –reverse reuse –add new code to a program without having to change the old code Calling the same method may yield different results. Implemented by virtual function

6. Introduction to Data Structures, Spring 2007 Slide- 6 California State University, Fresno What are Classes? Classes are blueprints and include –Data (attributes) contained within the class –Operations (methods) on those data Implementation is hidden to user of classes. –A lot of benefits

7. Introduction to Data Structures, Spring 2007 Slide- 7 California State University, Fresno More on Classes The basics elements of a class are –constructors Used in the creation of objects. Normally overloaded for the convenience of the class users –methods instance methods and class (static) methods –variables (or fields) instance variables and class variables (static) –constants instance (rare) and class (static) –other less common things including inner classes, static initializer blocks, non static initializer blocks

8. Introduction to Data Structures, Spring 2007 Slide- 8 California State University, Fresno Question? What is the difference between class and struct? –Visibility!

9. Introduction to Data Structures, Spring 2007 Slide- 9 California State University, Fresno Visibility Modifiers All parts of a class have visibility modifiers –public, protected, private Public: constructor, method, or field can be accessed outside of the class. –constructors and methods are generally public Private: part of the class is hidden and inaccessible by code outside of the class –data fields are generally private Protected: available to all friend classes and subclasses

10. Introduction to Data Structures, Spring 2007 Slide- 10 California State University, Fresno Example Declaration of “person” class: class Person { public: Person(); Person(char* firstName, char* lastName); SetName(char* firstName, char* lastName); char* GetName(); private: char firstName[20]; char lastName[20]; }

11. Introduction to Data Structures, Spring 2007 Slide- 11 California State University, Fresno Object - Instantiation Consider the Person class Person* p1 = new Person(); Person* p2 = new Person(); Person* p3 = new Person(“Ming”, “Li”); When the new operator is invoked control is transferred to the Person class and the specified constructor is executed, based on parameter matching (if multiple) Space(memory) is set aside for the new object's fields The memory address of the new object is passed back and stored in the object variable (pointer)

12. Introduction to Data Structures, Spring 2007 Slide- 12 California State University, Fresno Object – After Creation Every object created has its own instance of the variables declared in the class Data and methods of the class can be called by the. or - > operation Person p1; printf(“%s\n”,p1.firstName); /* Wrong!!!*/ p1.setName(“Ming”, “Li”); printf(“%s\n”,p1.getName());

13. Introduction to Data Structures, Spring 2007 Slide- 13 California State University, Fresno Class Variables and Class Methods Sometimes every object of a class does not need its own copy of a variable or constant –Usually used for constants The keyword static is used public static final int DEFAULT_SIDES = 6; Called directly with class name –Class::X;

14. Introduction to Data Structures, Spring 2007 Slide- 14 California State University, Fresno class user { private: int id; static int next_id; public: static int next_user_id() { next_id++; return next_id; } /* More stuff for the class user */ user() { id = user::next_id++; //or, id = user.next_user_id(); } }; int user::next_id = 0;

15. Introduction to Data Structures, Spring 2007 Slide- 15 California State University, Fresno Static Methods Static methods are normally utility methods or used to manipulate static variables Static methods may not manipulate any instance variables Called directly with class name –Class::method();

16. Introduction to Data Structures, Spring 2007 Slide- 16 California State University, Fresno Inheritance Classes can inherit from other classes Format public class Student extends Person Class Student: public Person Person is said to be –the parent class of Student –the super class of Student –the base class of Student –an ancestor of Student Student is said to be –a child class of Person –a sub class of Person –a derived class of Person –a descendant of Person

17. Introduction to Data Structures, Spring 2007 Slide- 17 California State University, Fresno Results of Inheritance Public class A Public class B extends A The subclass inherits (gains) all instance variables and instance methods of the super class automatically Additional methods can be added to class B (specialization) The sub class can replace (redefine, override) methods from the super class

18. Introduction to Data Structures, Spring 2007 Slide- 18 California State University, Fresno Overriding methods Any method that is not final may be overridden by a descendant class Same signature as method in ancestor May not reduce visibility May use the original method if simply want to add more behavior to existing –Super.X();

19. Introduction to Data Structures, Spring 2007 Slide- 19 California State University, Fresno Example Declaration of “person” class: class Person { public: Person(); Person(char* firstName, char* lastName); SetName(char* firstName, char* lastName); char* GetName(); private: char firstName[20]; char lastName[20]; }

20. Introduction to Data Structures, Spring 2007 Slide- 20 California State University, Fresno Example Declaration of “student” class: class Student:public Person { public: Student(); Student(char* firstName, char* lastName); SetProgram(char* program); char* GetProgarm(); SetGrade(int grade); int GetGrade(); private: char program[50]; int grade; }

21. Introduction to Data Structures, Spring 2007 Slide- 21 California State University, Fresno Example Usage of “Student” class Student s1; s1.SetName(“Ming”, “Li”); printf(“%s\n”,s1.GetName()); s1.SetProgram(“Computer Science”); printf(“%s\n”,s1.GetProgram()); S1.SetGrade(83); printf(“%d\n”,s1.GetGrade());

22. Introduction to Data Structures, Spring 2007 Slide- 22 California State University, Fresno Overriding example: class Pet {.... void speak(); }; void Pet::speak() { cout << "Growl" << endl; } class Rat: public Pet {... void speak(); }; void Rat::speak() { cout << "Rat noise" << endl; }

23. Introduction to Data Structures, Spring 2007 Slide- 23 California State University, Fresno Polymorphism Literally “having many forms” Object variables can refer to different types The actual type is known only at run-time C++ uses a virtual table which defines the message to method mapping for a given class

24. Introduction to Data Structures, Spring 2007 Slide- 24 California State University, Fresno Acknowledgement This slides is based partially on the two slides of the following webpage: http://www.cs.utexas.edu/~scottm/cs307/schedule.htm Some examples come from http://www.cplusplus.com/doc/language/tutorial