OOP Handouts (CS304) PDF - 20/08/2009

Object Oriented Programming (CS304) VU CS304-Handouts Last Updated: 20/08/2009 © Virtual University of Pakistan 1 Object Oriented Programming...

Object Oriented Programming (CS304) VU CS304-Handouts Last Updated: 20/08/2009 © Virtual University of Pakistan 1 Object Oriented Programming (CS304) VU LECTURE NO.01...................................................................................................................................8 01.1. INTRODUCTION....................................................................................................................8 01.2. WHAT IS A MODEL?...........................................................................................................10 01.3. OO MODELS:.....................................................................................................................11 01.4. OBJECT-ORIENTATION - ADVANTAGES...........................................................................12 01.5. WHAT IS AN OBJECT?........................................................................................................12 01.6. TANGIBLE AND INTANGIBLE OBJECTS.............................................................................12 01.7. SUMMARY:..........................................................................................................................13 LECTURE NO.02.................................................................................................................................15 02.1. INFORMATION HIDING:....................................................................................................15 02.2. ENCAPSULATION................................................................................................................16 02.3. INTERFACE..........................................................................................................................17 02.4. IMPLEMENTATION.............................................................................................................18 02.5. SEPARATION OF INTERFACE & IMPLEMENTATION.........................................................19 02.6. MESSAGES..........................................................................................................................19 02.7. SUMMARY...........................................................................................................................19 LECTURE NO.03.................................................................................................................................21 03.1. ABSTRACTION....................................................................................................................21 03.2. CLASSES..............................................................................................................................23 03.3. INHERITANCE.....................................................................................................................24 LECTURE NO.04.................................................................................................................................29 04.1. CONCEPTS RELATED WITH INHERITANCE.......................................................................29 04.2. GENERALIZATION..............................................................................................................29 04.3. SUB-TYPING (EXTENSION).................................................................................................31 04.4. SPECIALIZATION (RESTRICTION).....................................................................................32 04.5. OVERRIDING......................................................................................................................34 04.6. ABSTRACT CLASSES...........................................................................................................36 04.7. CONCRETE CLASSES..........................................................................................................38 LECTURE NO.05.................................................................................................................................40 05.3. SIMPLE ASSOCIATION.......................................................................................................49 05.4. COMPOSITION....................................................................................................................52 05.5. AGGREGATION...................................................................................................................53 LECTURE NO.06.................................................................................................................................55 06.1. CLASS COMPATIBILITY......................................................................................................55 06.2. POLYMORPHISM.................................................................................................................56 06.3. POLYMORPHISM IN OO MODEL.......................................................................................56 06.4. POLYMORPHISM – ADVANTAGES.....................................................................................57 06.5. OBJECT-ORIENTED MODELING AN EXAMPLE...................................................................58 LECTURE NO.07.................................................................................................................................65 07.1. CLASS..................................................................................................................................65 07.2. TYPE IN C++.......................................................................................................................65 07.3. ABSTRACTION....................................................................................................................66 07.4. DEFINING A NEW USER DEFINED TYPE...........................................................................66 07.5. OBJECT AND CLASS:..........................................................................................................68 07.6. ACCESSING MEMBERS........................................................................................................68 07.7. ACCESS SPECIFIERS............................................................................................................69 LECTURE NO.08.................................................................................................................................71 08.1. MEMBER FUNCTIONS........................................................................................................71 2 © Virtual University of Pakistan Object Oriented Programming (CS304) VU 08.2. DEFINING MEMBER FUNCTIONS...................................................................................... 71 08.3. INLINE FUNCTIONS............................................................................................................ 72 08.4. CONSTRUCTOR.................................................................................................................. 74 08.5. CONSTRUCTOR PROPERTIES............................................................................................. 74 08.6. DEFAULT CONSTRUCTOR................................................................................................. 75 08.7. CONSTRUCTOR OVERLOADING....................................................................................... 75 08.8. CONSTRUCTOR OVERLOADING....................................................................................... 77 08.9. COPY CONSTRUCTOR........................................................................................................ 78 08.10. SHALLOW COPY............................................................................................................ 79 08.11. DEEP COPY.................................................................................................................... 81 LECTURE NO.09................................................................................................................................ 83 09.1. SHALLOW COPY................................................................................................................. 84 09.2. DEEP COPY......................................................................................................................... 89 09.3. IMPORTANT POINTS ABOUT COPY CONSTRUCTOR:........................................................ 91 09.4. DESTRUCTOR..................................................................................................................... 92 09.5. ACCESSOR FUNCTIONS..................................................................................................... 93 09.6. THIS POINTER..................................................................................................................... 94 LECTURE NO.10................................................................................................................................ 97 10.1. USES OF THIS POINTER...................................................................................................... 97 10.2. SEPARATION OF INTERFACE AND IMPLEMENTATION..................................................... 97 10.3. COMPLEX NUMBER............................................................................................................ 97 10.4. CONST MEMBER FUNCTIONS.......................................................................................... 100 10.5. THIS POINTER AND CONST MEMBER FUNCTION.......................................................... 102 LECTURE NO.11.............................................................................................................................. 103 11.1. USAGE EXAMPLE OF CONSTANT MEMBER FUNCTIONS................................................. 103 11.2. DIFFERENCE BETWEEN INITIALIZATION AND ASSIGNMENT:....................................... 104 11.3. MEMBER INITIALIZER LIST............................................................................................. 104 11.4. CONST OBJECTS............................................................................................................... 105 11.5. STATIC VARIABLES.......................................................................................................... 107 LECTURE NO.12.............................................................................................................................. 110 12.1. ACCESSING STATIC DATA MEMBER.............................................................................. 111 12.2. LIFE OF STATIC DATA MEMBER..................................................................................... 111 12.3. STATIC MEMBER FUNCTION........................................................................................... 113 12.4. THIS POINTER AND STATIC MEMBER FUNCTIONS......................................................... 114 12.5. GLOBAL VARIABLE VS. STATIC MEMBERS.................................................................... 114 12.6. ARRAY OF OBJECTS......................................................................................................... 114 LECTURE NO.13.............................................................................................................................. 116 13.1. POINTER TO OBJECTS...................................................................................................... 116 13.2. BREAKUP OF NEW OPERATION....................................................................................... 117 13.3. CASE STUDY..................................................................................................................... 117 LECTURE NO.14.............................................................................................................................. 120 14.1. COMPOSITION.................................................................................................................. 120 LECTURE NO.15.............................................................................................................................. 128 15.1. AGGREGATION................................................................................................................ 132 15.2. FRIEND FUNCTIONS......................................................................................................... 135 LECTURE NO.16.............................................................................................................................. 138 16.1. OPERATOR OVERLOADING............................................................................................. 138 LECTURE NO.17.............................................................................................................................. 145 © Virtual University of Pakistan 3 Object Oriented Programming (CS304) VU 17.1. OVERLOADING ASSIGNMENT OPERATOR.....................................................................147 LECTURE NO.18...............................................................................................................................151 18.1. SELF ASSIGNMENT PROBLEM:.........................................................................................151 18.2. OTHER BINARY OPERATORS...........................................................................................152 18.3. FRIEND FUNCTIONS AND OPERATOR OVERLOADING..................................................153 LECTURE NO.19...............................................................................................................................154 19.1. STREAM INSERTION OPERATOR......................................................................................154 19.2. STREAM EXTRACTION OPERATOR..................................................................................154 19.3. OVERLOADING STREAM INSERTION OPERATOR..........................................................155 19.4. OVERLOADING STREAM EXTRACTION OPERATOR:......................................................156 19.5. OTHER BINARY OPERATORS:..........................................................................................157 LECTURE NO.20...............................................................................................................................159 20.1. SUBSCRIPT [] OPERATOR.................................................................................................160 20.2. OVERLOADING SUBSCRIPT [] OPERATOR......................................................................160 20.3. OVERLOADING FUNCTION () OPERATOR.......................................................................161 20.4. FUNCTION OPERATOR PERFORMING SUB STRING OPERATION,..................................161 20.5. UNARY OPERATORS.........................................................................................................162 LECTURE NO.21...............................................................................................................................164 21.1. BEHAVIOR OF ++ AND -- FOR PRE-DEFINED TYPES:.......................................................164 21.2. POST-INCREMENT OPERATOR:........................................................................................165 21.3. TYPE CONVERSION..........................................................................................................166 21.4. USER DEFINED TYPES:......................................................................................................169 21.5. DRAWBACKS OF TYPE CONVERSION OPERATOR:.........................................................170 LECTURE NO.22...............................................................................................................................171 22.1. PRACTICAL IMPLEMENTATION OF INHERITANCE IN C++.............................................171 22.2. INHERITANCE IN CLASSES...............................................................................................171 22.3. UML NOTATION.............................................................................................................171 22.4. INHERITANCE IN C++......................................................................................................171 22.5. “IS A” RELATIONSHIP.....................................................................................................172 LECTURE NO.23...............................................................................................................................179 23.1. ACCESSING BASE CLASS MEMBER FUNCTIONS IN DERIVED CLASS:.............................179 23.2. “PROTECTED” ACCESS SPECIFIER:...................................................................................181 23.3. “IS A” RELATIONSHIP.....................................................................................................182 23.4. STATIC TYPE.....................................................................................................................185 LECTURE NO.24...............................................................................................................................187 24.1. MODIFIED DEFAULT CONSTRUCTOR.............................................................................195 LECTURE NO.25...............................................................................................................................203 25.1. OVERLOADING VS. OVERRIDING...................................................................................203 25.2. HIERARCHY OF INHERITANCE.........................................................................................207 LECTURE NO.26...............................................................................................................................209 26.1. BASE INITIALIZATION.......................................................................................................209 26.2. TYPES OF INHERITANCE...................................................................................................210 26.3. PRIVATE INHERITANCE...................................................................................................212 LECTURE NO.27...............................................................................................................................214 27.1. SPECIALIZATION (RESTRICTION)...................................................................................214 27.2. PROTECTED INHERITANCE..............................................................................................218 27.3. PROPERTIES OF PROTECTED INHERITANCE...................................................................219 4 © Virtual University of Pakistan Object Oriented Programming (CS304) VU LECTURE NO.28.............................................................................................................................. 221 28.1. VIRTUAL FUNCTIONS...................................................................................................... 221 28.2. VIRTUAL FUNCTIONS:..................................................................................................... 226 28.3. SHAPE HIERARCHY.......................................................................................................... 226 28.4. STATIC VS DYNAMIC BINDING...................................................................................... 227 LECTURE NO.29.............................................................................................................................. 229 29.1. ABSTRACT CLASSES........................................................................................................ 229 29.2. CONCRETE CLASSES........................................................................................................ 230 29.3. ABSTRACT CLASSES IN C++........................................................................................... 230 29.4. PURE VIRTUAL FUNCTIONS............................................................................................ 230 29.5. SHAPE HIERARCHY.......................................................................................................... 230 29.6. VIRTUAL DESTRUCTORS................................................................................................. 232 29.7. VIRTUAL FUNCTIONS – USAGE...................................................................................... 235 29.8. V TABLE............................................................................................................................ 236 29.9. DYNAMIC DISPATCH (DYNAMIC BINDING)................................................................. 239 LECTURE NO.30.............................................................................................................................. 240 30.1. POLYMORPHISM – CASE STUDY: A SIMPLE PAYROLL APPLICATION.......................... 240 30.2. SHAPE HIERARCHY REVISITED:...................................................................................... 243 LECTURE NO.31.............................................................................................................................. 247 31.1. MULTIPLE INHERITANCE................................................................................................. 247 31.2. PROBLEMS IN MULTIPLE INHERITANCE......................................................................... 248 31.3. VIRTUAL INHERITANCE.................................................................................................. 253 LECTURE NO.32.............................................................................................................................. 255 32.1. GENERIC PROGRAMMING............................................................................................... 256 32.2. TEMPLATES....................................................................................................................... 256 32.3. FUNCTION TEMPLATES................................................................................................... 257 LECTURE NO.33.............................................................................................................................. 261 33.1. MULTIPLE TYPE ARGUMENTS......................................................................................... 261 33.2. USER-DEFINED TYPES..................................................................................................... 261 33.3. OVERLOADING VS. TEMPLATES..................................................................................... 262 33.4. TEMPLATE ARGUMENTS AS POLICY:.............................................................................. 263 33.5. FIRST SOLUTION:............................................................................................................. 263 33.6. SECOND SOLUTION:........................................................................................................ 264 33.7. THIRD SOLUTION............................................................................................................ 264 33.8. DEFAULT POLICY............................................................................................................. 265 LECTURE NO.34.............................................................................................................................. 267 34.1. GENERIC ALGORITHMS.................................................................................................. 267 34.2. CLASS TEMPLATES........................................................................................................... 269 34.3. EXAMPLE – CLASS TEMPLATE......................................................................................... 270 LECTURE NO.35.............................................................................................................................. 273 35.1. MEMBER TEMPLATES:..................................................................................................... 273 35.2. CLASS TEMPLATE SPECIALIZATION............................................................................... 275 LECTURE NO.36.............................................................................................................................. 279 36.1. MEMBER TEMPLATES REVISITED................................................................................... 279 36.2. PARTIAL SPECIALIZATION:............................................................................................. 280 36.3. FUNCTION TEMPLATES................................................................................................... 281 36.4. COMPLETE SPECIALIZATION........................................................................................... 282 36.5. USING DIFFERENT SPECIALIZATIONS............................................................................ 283 36.6. NON-TYPE PARAMETERS................................................................................................. 283 © Virtual University of Pakistan 5 Object Oriented Programming (CS304) VU 36.7. EXAMPLE – TEMPLATE CLASS ARRAY.............................................................................283 36.8. DEFAULT NON-TYPE PARAMETERS................................................................................284 36.9. DEFAULT TYPE PARAMETERS..........................................................................................285 LECTURE NO.37...............................................................................................................................285 37.1. RESOLUTION ORDER.......................................................................................................285 37.2. FUNCTION TEMPLATE OVERLOADING...........................................................................287 37.3. RESOLUTION ORDER.......................................................................................................287 37.4. TEMPLATES AND INHERITANCE......................................................................................287 37.5. DERIVATIONS IN CASE OF A GENERAL TEMPLATE CLASS............................................288 LECTURE NO.38...............................................................................................................................292 38.1. TEMPLATES AND FRIENDS...............................................................................................292 38.2. TEMPLATES AND FRIENDS – RULE 1...............................................................................292 38.3. TEMPLATES AND FRIENDS – RULE 2...............................................................................293 38.4. TEMPLATES AND FRIENDS – RULE 3...............................................................................295 38.5. TEMPLATES AND FRIENDS – RULE 4...............................................................................296 LECTURE NO.39...............................................................................................................................299 39.1. TEMPLATES & STATIC MEMBERS...................................................................................299 39.2. TEMPLATES – CONCLUSION............................................................................................300 39.3. GENERIC ALGORITHMS REVISITED................................................................................301 39.4. GENERIC ALGORITHMS REVISITED................................................................................301 39.5. GENERIC ALGORITHM.....................................................................................................303 39.6. PROBLEMS........................................................................................................................304 LECTURE NO.40...............................................................................................................................305 40.1. CURSORS..........................................................................................................................305 40.2. ITERATORS........................................................................................................................308 LECTURE NO.41...............................................................................................................................312 41.1. STANDARD TEMPLATE LIBRARY:....................................................................................312 41.2. STL CONTAINERS............................................................................................................312 41.3. COMMON FUNCTIONS FOR ALL CONTAINERS..............................................................317 41.4. FUNCTIONS FOR FIRST-CLASS CONTAINERS.................................................................318 41.5. CONTAINER REQUIREMENTS..........................................................................................319 LECTURE NO.42...............................................................................................................................320 42.1. ITERATORS........................................................................................................................320 42.2. ITERATOR CATEGORIES...................................................................................................320 42.3. ITERATOR SUMMARY:......................................................................................................320 42.4. CONTAINER AND ITERATOR TYPES:...............................................................................321 42.5. SEQUENCE CONTAINERS.................................................................................................321 42.6. ASSOCIATIVE CONTAINERS............................................................................................322 42.7. CONTAINER ADAPTERS...................................................................................................322 42.8. ITERATOR OPERATIONS..................................................................................................322 42.9. ALGORITHMS...................................................................................................................326 LECTURE NO.43...............................................................................................................................329 43.1. EXAMPLE – ABNORMAL TERMINATION.........................................................................329 43.2. GRACEFUL TERMINATION...............................................................................................330 43.3. ERROR HANDLING...........................................................................................................330 43.4. EXCEPTION HANDLING...................................................................................................333 43.5. EXCEPTION HANDLING PROCESS...................................................................................333 LECTURE NO.44...............................................................................................................................336 44.1. STACK UNWINDING........................................................................................................336 6 © Virtual University of Pakistan Object Oriented Programming (CS304) VU LECTURE NO.45.............................................................................................................................. 343 45.1. RESOURCE MANAGEMENT............................................................................................. 343 © Virtual University of Pakistan 7 Object Oriented Programming (CS304) VU Lecture No.01 01.1. Introduction Course Objective: Objective of this course is to make students familiar with the concepts of object oriented programming. These concepts will be reinforced by their implementation in C++. Course Contents: The main topics that we will study in the 45 lectures of this course are given below, Object Orientation Objects and Classes Overloading Inheritance Polymorphism Generic Programming Exception Handling Introduction to Design Patterns Recommended Text Book: C++ How to Program ( Deitel & Deitel ) Reference Books: 1. Object-Oriented Software Engineering By Jacobson, Christerson, Jonsson, Overgaard (For object oriented programming introductory concepts) 2. The C++ Programming Language By Bjarne Stroustrup (For better c++ understanding) 8 © Virtual University of Pakistan Object Oriented Programming (CS304) VU Object-Orientation (OO) What is Object-Orientation? It is a technique in which we visualize our programming problems in the form of objects and their interactions as happens in real life. Examples: We have different objects around us in our real life that interact with each other to perform different operations for example, A Person A House A Tree A Car Different Objects These objects interact with each other to perform different operations, Lives in Ali House Drives Car Tree Take another example of a School; the objects in a school are student, teacher, books, pen ,school bag, classroom, parents, playground and so on… , Objects in a School © Virtual University of Pakistan 9 Object Oriented Programming (CS304) VU Teacher Student School Bag Book Pen Playground Parents Classroom Library Suppose we want to develop a fee collection system for a school for this we will need to find out related objects and their interactions as happens in real life. In this way we can say that object orientation makes it easier for us to solve our real world problems by thinking solution of the problem in terms of real world objects. So we can say that in our daily life everything can be taken as an object that behaves in a certain way and has certain attributes. In object orientation we move our concentration to objects in contrast to procedural paradigm in which we simply write our code in functions and call them in our main program. 01.2. What is a Model? A model is an abstraction of something real or conceptual. We need models to understand an aspect of reality. Model Examples 10 © Virtual University of Pakistan Object Oriented Programming (CS304) VU Highway maps Architectural models Mechanical models 01.3. OO Models: In the context of programming models are used to understand the problem before starting developing it. We make Object Oriented models showing several interacting objects to understand a system given to us for implementation. Example 1– Object Oriented Model lives-in Ali House drives Car Tree Objects Interactions Ali, Car, House, Tree Ali lives in the house Ali drives the car Example 2– Object Oriented Model (A School Model) © Virtual University of Pakistan 11 Object Oriented Programming (CS304) VU A School Model Teaches Plays-in Teacher Student Playground Has Book Pen School Bag Objects Interactions Teacher, Student, School Bag, Pen, Teacher teaches Student. Book Playground Student has School Bag, Book and Pen 01.4. Object-Orientation - Advantages As Object Oriented Models map directly to reality as we have seen in examples above therefore, We can easily develop an object oriented model for a problem. Everyone can easily understand an object oriented model. We can easily implement an object oriented model for a problem using any object oriented language like c++ using its features1 like classes, inheritance, virtual functions and so on… 01.5. What is an Object? An object is, 1. Something tangible (Ali, School, House, Car). 2. Something conceptual (that can be apprehended intellectually for example time, date and so on…). An object has, 1. State (attributes) 2. Well-defined behavior (operations) 3. Unique identity 01.6. Tangible and Intangible Objects Examples of Tangible Objects: 1 We will study these features in detail in this course 12 © Virtual University of Pakistan Object Oriented Programming (CS304) VU Ali is a tangible object, having some characteristics (attributes) and behavior as given below, Ali Characteristics (attributes) Behaviour (operations) Name Walks Age Eats We will identify Ali using his name. Car is also a tangible object having some characteristics (attributes) and behavior given below, Car State (attributes) Behavior (operations) Color Accelerate Model Start Car Change Gear We can identify Car using its registration number Examples of Intangible Objects (also called as conceptual objects): Time is an intangible (conceptual) object Time State (attributes) Behavior (operations) Hours Set/Get Hours Seconds Set/Get Seconds Minutes Set/Get Minutes We will assign our own generated unique ID in the model for Time object Date is also an intangible (conceptual) object State (attributes) Behavior (operations) Year Set/Get Year Day Set/Get Day Month Set/Get Month We will assign our own generated unique ID in the model for Date object. 01.7. Summary: © Virtual University of Pakistan 13 Object Oriented Programming (CS304) VU Model is the abstraction of some real word scenario. It helps us to understand that scenario. Object oriented model of any scenario (problem) describes that scenario (problem) in the form of interacting objects. We use Object Orientation because it helps us in mapping real world problem in a programming language. Object Orientation is achieved using objects and their relationships. Properties of an object are described using its data members and behavior of an object is described using its functions. Objects may be tangible (physical) or intangible (also called conceptual or virtual). Generally when we have given a certain problem description, nouns in that problem description are candidates for becoming objects of our system. There may be more than one aspects of an object It is not necessary that every object has a specific role in implementation of a problem there may be some objects without any role, like school parking in our school. It is easier to develop programs using Object Oriented Programming because it is closer to real life. 14 © Virtual University of Pakistan Object Oriented Programming (CS304) VU Lecture No.02 Lecture Contents 1. Information Hiding 2. Encapsulation 3. Interface 4. Implementation 5. Separation of Interface & Implementation 6. Messages 02.1. Information Hiding: Information hiding is one of the most important principles of OOP inspired from real life which says that all information should not be accessible to all persons. Private information should only be accessible to its owner. By Information Hiding we mean “Showing only those details to the outside world which are necessary for the outside world and hiding all other details from the outside world.” Real Life Examples of Information Hiding 1. Ali’s name and other personal information is stored in his brain we can’t access this information directly. For getting this information we need to ask Ali about it and it will be up to Ali how much details he would like to share with us. 2. An email server may have account information of millions of people but it will share only our account information with us if we request it to send anyone else accounts information our request will be refused. 3. A phone SIM card may store several phone numbers but we can’t read the numbers directly from the SIM card rather phone-set reads this information for us and if the owner of this phone has not allowed others to see the numbers saved in this phone we will not be able to see those phone numbers using phone. In object oriented programming approach we have objects with their attributes and behaviors that are hidden from other classes, so we can say that object oriented programming follows the principle of information hiding. In the perspective of Object Oriented Programming Information Hiding is, “Hiding the object details (state and behavior) from the users” Here by users we mean “an object” of another class that is calling functions of this class using the reference of this class object or it may be some other program in which we are using this class. Information Hiding is achieved in Object Oriented Programming using the following principles, © Virtual University of Pakistan 15 Object Oriented Programming (CS304) VU All information related to an object is stored within the object It is hidden from the outside world It can only be manipulated by the object itself Advantages of Information Hiding Following are two major advantages of information hiding, It simplifies our Object Oriented Model: As we saw earlier that our object oriented model only had objects and their interactions hiding implementation details so it makes it easier for everyone to understand our object oriented model. It is a barrier against change propagation As implementation of functions is limited to our class and we have only given the name of functions to user along with description of parameters so if we change implementation of function it doesn’t affect the object oriented model. We can achieve information hiding using Encapsulation and Abstraction, so we see these two concepts in detail now, 02.2. Encapsulation Encapsulation means “we have enclosed all the characteristics of an object in the object itself” Encapsulation and information hiding are much related concepts (information hiding is achieved using Encapsulation) We have seen in previous lecture that object characteristics include data members and behavior of the object in the form of functions. So we can say that Data and Behavior are tightly coupled inside an object and both the information structure and implementation details of its operations are hidden from the outer world. Examples of Encapsulation Consider the same example of object Ali of previous lecture we described it as follows, 16 © Virtual University of Pakistan Object Oriented Programming (CS304) VU Ali Characteristics (attributes) Name Age Behavior (operations) Walks Eats You can see that Ali stores his personal information in itself and its behavior is also implemented in it. Now it is up to object Ali whether he wants to share that information with outside world or not. Same thing stands for its behavior if some other object in real life wants to use his behavior of walking it can not use it without the permission of Ali. So we say that attributes and behavior of Ali are encapsulated in it. Any other object don’t know about these things unless Ali share this information with that object through an interface, Same concept also applies to phone which has some data and behavior of showing that data to user we can only access the information stored in the phone if phone interface allow us to do so. Advantages of Encapsulation The following are the main advantages of Encapsulation, a. Simplicity and clarity As all data and functions are stored in the objects so there is no data or function around in program that is not part of any object and is this way it becomes very easy to understand the purpose of each data member and function in an object. b. Low complexity As data members and functions are hidden in objects and each object has a specific behavior so there is less complexity in code there will be no such situations that a functions is using some other function and that functions is using some other function. c. Better understanding Everyone will be able to understand whole scenario by simple looking into object diagrams without any issue as each object has specific role and specific relation with other objects. 02.3. Interface © Virtual University of Pakistan 17 Object Oriented Programming (CS304) VU Interface is a set of functions of an object that he wants to expose to other objects. As we discussed previously that data and behavior of each object is hidden in that object it self so we have to use the concept of interface of the object to expose its behavior to outer word objects. Different objects may need different functions of an object so interface of an object may be different for different objects. Interfaces are necessary for object communication. Each object provides interface/s (operations) to other objects through these interfaces other objects communicate with this object. Example – Interface of a Car Steer Wheels Accelerate Change Gear Apply Brakes Turn Lights On/Off Example – Interface of a Phone Input Number Place Call Disconnect Call Add number to address book Remove number Update number 02.4. Implementation It is actual implementation of the behavior of the object in any Object Oriented language. It has two parts, Internal data structures to hold an object state that will be hidden from us it will store values for an object data members. Functionality in the form of member functions to provide required behavior. Examples of Implementation a. Gear Box in car system Consider object Gear Box in car system it has a certain structure and functionality. When this object will be implemented it will have two things, Physical structure of the gear box Functionality implemented in this structure to change gear. Both these things are part of implementation. 18 © Virtual University of Pakistan Object Oriented Programming (CS304) VU So it has, Data Structure in the form of Mechanical structure of gear box Functionality mechanism to change gear b. Address Book in a Phone Similarly take the example of contact details saved in the SIM of a phone, In that case we can say physical structure of SIM card as Data Structure And Read/write operations provided by the phone as Functionality. 02.5. Separation of Interface & Implementation As discussed earlier we only show interface of an object to outside world and hide actual implementation from outside world. The benefit of using this approach is that our object interface to outside word becomes independent from inside implementation of that interface. This is achieved through the concepts of encapsulation and information hiding. Real Life example of separation of interface and implementations
Driver has a standard interface to drive a car and using that interface he drive can drive any car regardless of its model or type whatever engine type it has or whatever type of fuel it is using. 02.6. Messages Objects communicate through messages they send messages (stimuli) by invoking appropriate operations on the target object. The number and kind of messages that can be sent to an object depends upon its interface Examples – Messages A Person sends message (stimulus) “stop” to a Car by applying brakes A Person sends message “place call” to a Phone by pressing appropriate button 02.7. Summary Information hiding is achieved through encapsulation. Encapsulation and Information Hiding are related to each other. Interface of an object provides us the list of available functions. An object may have more than one interface. Interface and implementation are separated from each other to achieve Information Hiding. Objects communicate with each other using messages. © Virtual University of Pakistan 19 Object Oriented Programming (CS304) VU Useful Links: http://www.alice.org/ A Graphical Programming Environment to teach Computer Programming. 20 © Virtual University of Pakistan Object Oriented Programming (CS304) VU Lecture No.03 Lecture Contents: Abstraction Classes Inheritance Major benefits of inheritance (Reuse) 03.1. Abstraction Real life objects have a lot of attributes and many kind of behaviors but most of the time we are interested in only that part of the objects that is related to the problem we are currently going to solve, for example in implementing a school system we don’t need to take care of the personnel life of a student or a teacher as it will not effect our system in any way so we will see these objects in the perspective of school system and will ignore their other characteristics, this concept is called “Abstraction”. Abstraction is a way to cope with complexity and it is used to simplify things. Principle of abstraction: “Capture only those details about an object that are relevant to current perspective” Abstraction Example: Suppose we want to implement abstraction for the following statement, “Ali is a PhD student and teaches BS students” Here object Ali has two perspectives one is his student perspective and second is his teacher perspective. We can sum up Ali’s attributes as follows, Name Age Student Roll No Year of Study CGPA Employee ID Designation Salary As you can see out of all these listed attributes some belong to Ali’s student perspective(Roll No, CGPA, Year of study) and some belong to Ali’s teacher perspective(Employee ID, Designation, Salary). Similarly we can sum up Ali’s behavior as follows, Study DevelopExam GiveExam © Virtual University of Pakistan 21 Object Oriented Programming (CS304) VU TakeExam PlaySports Eat DeliverLecture Walk As was the case with attributes of object Ali, its behavior can also be divided in Ali’s student perspective as well as Ali’s teacher perspective. Student’s Perspective Attributes: - Name - Employee ID - Student Roll No - Designation - Year of Study - Salary - CGPA - Age Behaviour: - Study - DevelopExam - GiveExam - TakeExam - PlaySports - Eat - DeliverLecture - Walk Teacher’s Perspective Attributes: - Name - Employee ID - Student Roll No - Designation - Year of Study - Salary - CGPA - Age Behaviour: - Study - DevelopExam - GiveExam - TakeExam - PlaySports - Eat - DeliverLecture - Walk A cat can be viewed with different perspectives Ordinary Perspective Surgeon’s Perspective A pet animal with A being with Four Legs A Skeleton A Tail Heart Two Ears Kidney Sharp Teeth Stomach 22 © Virtual University of Pakistan Object Oriented Programming (CS304) VU A car can be viewed with different perspectives Driver’s View Engineer’s View Abstraction – Advantages Abstraction has following major advantages, 1. It helps us understanding and solving a problem using object oriented approach as it hides extra irrelevant details of objects. 2. Focusing on single perspective of an object provides us freedom to change implementation for other aspects of for an object later. Similar to Encapsulation Abstraction is also used for achieving information hiding as we show only relevant details to related objects, and hide other details. 03.2. Classes In OOP we create a general sketch for each kind of objects and then we create different instances using this sketch we call this sketch or prototype or map as “class”. All objects of same kind exhibit identical characteristics (information structure and behavior) however they have data of their own. Class –Example 1 Consider the objects given below, Ali studies mathematics Anam studies physics Sohail studies chemistry Each one is a Student so we say these objects are instances of the Student class. Class –Example 2 Consider the objects given below, Ahsan teaches mathematics Aamir teaches computer science © Virtual University of Pakistan 23 Object Oriented Programming (CS304) VU Atif teaches physics Each one is a teacher so we say these objects are instances of the Teacher class Class Representation: we can represent a class using a rectangle as follows, (Class Name) (Attributes) (Operations) (Class Name) Normal Form Suppressed Form Class Example: Circle Circle center radius draw computeArea Circle Normal Form Suppressed Form Class Example: Person Person name age gender eat walk Person Normal Form Suppressed Form 03.3. Inheritance 24 © Virtual University of Pakistan Object Oriented Programming (CS304) VU A child inherits characteristics of its parents, besides inherited characteristics, a child may have its own unique characteristics Inheritance in Classes If a class B inherits from class A then it contains all the characteristics (information structure and behaviour) of class A The parent class is called base class and the child class is called derived class Besides inherited characteristics, derived class may have its own unique characteristics Person Student Doctor Teacher Shape Line Triangle Circle Inheritance – “IS A” or “IS A KIND OF” Relationship Each derived class is a kind of its base class © Virtual University of Pakistan 25 Object Oriented Programming (CS304) VU Person name age gender eat walk Student Teacher Doctor program designation designation studyYear salary salary study teach checkUp heldExam takeExam prescribe Here, Student IS A Person Teacher IS A Person Doctor IS A Person Shape color coord draw rotate setColor Triangle Circle radius Line angle draw length draw computeArea computeArea draw Here, Circle IS A Shape Line IS A Shape Triangle IS A Shape Inheritance – Advantages 1. Reuse 26 © Virtual University of Pakistan Object Oriented Programming (CS304) VU 2. Less redundancy 3. Increased maintainability Reuse with Inheritance Main purpose of inheritance is reuse, we can easily add new classes by inheriting from existing classes. Select an existing class closer to the desired functionality, create a new class and inherit it from the selected class, add to and/or modify the inherited functionality Shape color coord draw rotate setColor Triangle Circle radius Line angle draw length draw computeArea computeArea draw Person name age gender eat walk Student Teacher Doctor program designation designation studyYear salary salary study teach checkUp heldExam takeExam prescribe © Virtual University of Pakistan 27 Object Oriented Programming (CS304) VU Person name age gender eat walk Student Teacher Doctor program designation designation studyYear salary salary study teach checkUp heldExam takeExam prescribe 28 © Virtual University of Pakistan Object Oriented Programming (CS304) VU Lecture No.04 Lecture Contents Generalization Sub typing (extension) Specialization (restriction) Overriding Abstract classes Concrete classes Recap – Inheritance Derived class inherits all the characteristics of the base class Besides inherited characteristics, derived class may have its own unique characteristics Major benefit of inheritance is reuse 04.1. Concepts Related with Inheritance o Generalization o Subtyping (extension) o Specialization (restriction) 04.2. Generalization In OO models, some classes may have common characteristics. We extract these features into a new class and inherit original classes from this new class. There are many objects with common characteristics in object model. The common characteristics (attributes and behaviour) of all these objects are combined in a single general class. Base class encapsulates the idea of commonality of derived classes. Base class is general class representing common behaviour of all derived classes. This concept is known as Generalization. It reduces the redundancy and gives us reusability, using generalization our solution becomes less complex. In generalization there should be “Is a Kind of Relationship” (also called “Is A relationship”) between base and child classes. Example: Line, Circle and Triangle © Virtual University of Pakistan 29 Object Oriented Programming (CS304) VU Line Circle Triangle color color color vertices vertices vertices length radius angle move move move setColor setColor setColor getLength computeArea computeArea Line is shape Circle is a shape Triangle is a shape Shape color vertices move setColor Triangle Circle radius Line angle computeArea length computeArea getLength Common attributes Color vertices Common behaviour Set Color, Move Example: Student Doctor and Teacher 30 © Virtual University of Pakistan Object Oriented Programming (CS304) VU Student Teacher Doctor name name name age age age gender gender gender program designation designation studyYear salary salary study teach checkUp heldExam takeExam prescribe eat eat eat walk walk walk Person name age gender eat walk Student Teacher Doctor program designation designation studyYear salary salary study teach checkUp heldExam takeExam prescribe Common attributes, Common behaviour Name, age, gender Eat, Walk Sub-typing & Specialization We want to add a new class to an existing model We have developed an existing class hierarchy Find an existing class that already implements some of the desired state and behaviour Inherit the new class from this class and add unique behaviour to the new class 04.3. Sub-typing (Extension) Sub-typing means that derived class is behaviourally compatible with the base class Derived class has all the characteristics of base class plus some extra characteristics Behaviourally compatible means that base class can be replaced by the derived class © Virtual University of Pakistan 31 Object Oriented Programming (CS304) VU Sub-typing (Extension) - Example Person Shape name color age vertices gender setColor eats move walks Circle Student radius program studyYear computeCF computeArea study takeExam Circle is extending the behaviour of Student has two extra attributes program shape, it is extending attributes of shape and studyYear by adding radius similarly it is extending Similarly it has extended behaviour by behaviour of shape by adding compute adding study and takeExam. Circumference and compute Area. Subtyping and generalization are related concepts, Subtyping (extension) and generalization is a way to look same thing in two ways. Sub typing is looking at things from Top to bottom whereas in generalization we look at things from bottom to top. 04.4. Specialization (Restriction) We want to add a class to existing hierarchy of classes having many similarities to already existing classes but some part of its behaviour is different or restricted. In that case we will use the concept of specialization. Specialization means that derived class is behaviourally incompatible with the base class Behaviourally incompatibility means that base class can’t always be replaced by the derived class Derived class has some different of restricted characteristics than of base class. Example – Specialization (Restriction) Suppose we want to add one more class of Adult for some special requirement like for ID card generation such that it is a person but its age is greater than 18 and having all other behaviour of that of person class. One solution is that we write 32 © Virtual University of Pakistan Object Oriented Programming (CS304) VU another class from beginning and write all code of person again in it with age limit, but better solution is that we derive adult class from person class and restrict age in that class as shown below in diagram, Person age : [0..100] … setAge( a ) age = a … Adult If age < 18 then age : [18..100] error … else age = a setAge( a ) … Similarly Natural Numbers2 are also Integers3 with the restriction that natural numbers set can NOT contain zero or negative integers it consists of only positive integers so we can implement this relationship also as specialization, 2 Natural numbers: positive integers only (numbers from 1 to …….onwards) 3 Integers: all positive and negative numbers (…..-3 , -2 , -1 , 0 , 1 , 2 , 3………) © Virtual University of Pakistan 33 Object Oriented Programming (CS304) VU IntegerSet … add( elem ) add element to the … set If elem < 1 then NaturalSet error else … add element to add( elem ) the set … Add method behaviour is present in both base and derived classes but derived class behaviour is different in derived class. Derived class will not exhibit the behaviour of base class but it is overriding behaviour of base class with its own behaviour. 04.5. Overriding A class may need to override the default behaviour provided by its base class Derived class overrides the behaviour of its base class. Reasons for overriding Provide behaviour specific to a derived class (specialization) Extend the default behaviour (extension) Restrict the default behaviour (restriction) Improve performance It is used for the implementation of inheritance. Example – Specific Behaviour (Specialization) 34 © Virtual University of Pakistan Object Oriented Programming (CS304) VU Shape color vertices draw move setColor Circle Line Triangle radius length angle draw draw draw computeArea computeArea Example – Extention Window width height open close draw 1- Invoke Window’s DialogBox draw 2- draw the dialog controls box enable draw Example – Restriction © Virtual University of Pakistan 35 Object Oriented Programming (CS304) VU IntegerSet … add( elem ) Add element to … the set If elem < 1 then NaturalSet give error else … Add element add( elem ) to the set … Example – Improve Performance Class Circle overrides rotate operation of class Shape with a Null operation. Shape color coord draw rotate setColor Circle radius draw rotate 04.6. Abstract Classes In our examples we made classes for shape and person. These are abstract concepts and the classes we make against abstract concepts are called abstract classes. They are present at or near the top in the class hierarchy to present most generalized behaviour. An abstract class implements an abstract concept Main purpose is to be inherited by other classes Can’t be instantiated Promotes reuse 36 © Virtual University of Pakistan Object Oriented Programming (CS304) VU Abstract Classes - Example I Shape color vertices draw move setColor Circle Line Triangle Here, Shape is an abstract class Abstract Class Shape Concrete Classes Circle Line Triangle …. Abstract Classes - Example II Person name age gender eat walk Student Doctor Teacher Here, Person is an abstract class Abstract Class Person Concrete Classes Student Teacher Doctor Engineer Director …. Abstract Classes - Example III © Virtual University of Pakistan 37 Object Oriented Programming (CS304) VU Vehicle color model accelerate applyBrakes Car Truck Bus Here, Vehicle is an abstract class Abstract Class Vehicle Concrete Classes Car Bus Truck …. Abstract Classes can not exist standalone in an object model While making object model we start by finding out objects in our object model and then we find out objects having common attributes and make them in the form of general classes at the top of class hierarchies. 04.7. Concrete Classes The entities that actually we see in our real world are called concrete objects and classes made against these objects are called concrete classes. A concrete class implements a concrete concept These are used to instantiate objects in our programs Provides implementation details specific to the domain context Concrete Classes - Example I Person Student Doctor program Teacher studyYear study heldExam 38 © Virtual University of Pakistan Object Oriented Programming (CS304) VU Here Student, Teacher and Doctor are concrete classes Concrete Classes - Example II Vehicle Car Truck Bus capacity load unload Here Car, Bus and Truck are concrete classes A concrete class may exist in an object model independently Concrete classes mostly lie below the top of class hierarchy in a good object model. If there is an abstract class then hierarchy exists in the object model as there will definitely be some concrete classes as well derived from this abstract class otherwise there is no use of abstract class. Glossary: a. Natural numbers: numbers from 1 to …….onwards b. Integers: all positive and negative numbers …..-3,-2,-1,0,1,2,3……… c. Whole numbers: numbers from 0 ,1 ,2, 3 ….onwards (natural no’s including 0) Some times whole numbers are also called numbers without fractional part. © Virtual University of Pakistan 39 Object Oriented Programming (CS304) VU Lecture No.05 Multiple Inheritance Inheritance: We saw inheritance purposes in last lecture Generalization Extention or sub typing Specialization or restriction Abstract and concrete classes, former is used to represent abstract concepts later is used to represent concrete concepts. Overriding derived classes override inherited classes (base classes) behaviour. Overriding is used for Specialization, Extention, Restriction, and Performance. 05.1. Multiple Inheritance Sometimes we want to reuse characteristics of more than one parent class, in that case we need to inherit a class from more than one classes. Example 1– Multiple Inheritance Consider the example of an imaginary specie Mermaid used in fairy tales that lives in water having features both of a women as well as of a fish, In Object Oriented programming perspective Mermaid can be derived from two classes Women and Fish. Woman Fish Mermaid C++ Code: class Fish { }; class Woman { }; 40 © Virtual University of Pakistan Object Oriented Programming (CS304) VU class Mermaid : public Woman , public Fish { }; Our Mermaid class inherits features of both woman and fish suppose our woman class has method wald() and fish cclass has method swim then our mermaid class can use both methods i.e can walk as well as can swim. Woman Fish void walk() void swim() Mermaid c++ code: #include #include using namespace std; class Fish { public: void swim(){ cout