Introduction to Data Structures, Spring 2007 Slide- 1 California State University, Fresno Introduction to Data Structure Object Oriented Programming Concepts

Introduction to Data Structures, Spring 2007 Slide- 1

California State University, Fresno

Introduction to Data Structure

Object Oriented Programming Concepts

Ming LiDepartment of Computer Science

California State University, FresnoFall 2006



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



Object Oriented ProgrammingEncapsulation

• Hiding information within one abstraction

• Achieved via classes and objects.



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



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



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



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



Question?

• What is the difference between class and struct?– Visibility!



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



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];

}



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)



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());



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;



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;



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();



Inheritance• Classes can inherit from other classes• Format

public class Student extends PersonClass 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



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



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();



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];

}



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;

}



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());



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;}



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



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

Documents

Introduction to Data Structures, Spring 2007 Slide- 1 California State University, Fresno Introduction to Data Structure Object Oriented Programming Concepts