Object Oriented Programming in C MAITRAYEE MUKERJI Recap
Object Oriented Programming in C++ MAITRAYEE MUKERJI
Recap: Object Oriented Approach �Four major elements: Abstraction Encapsulation Modularity Hierarchy �Three minor elements: Typing Concurrency Persistence
Abstraction Motor Bike Chiku Bajaj Apple Truck Mango Maruti Wagon-R Car Scooter Jeep Lemon Banana
Abstraction �Dahl, Dijkstra, and Hoare suggest that “abstraction arises from a recognition of similarities between certain objects, situations, or processes in the real world, and the decision to concentrate upon these similarities and to ignore for the time being the differences” [42].
Abstraction �An abstraction denotes the essential characteristics of an object that distinguish it from all other kinds of objects and thus provide crisply defined conceptual boundaries, relative to the perspective of the viewer.
Abstraction: Perspective of User Bank Customer Parent Child Name Class Roll No Mobile No Name Pan No Acct Type Loyalty Program Member Employee Name Card No Points Name Id No Mobile No Tax Payer Name Pan No Annual Return
Abstraction �An abstraction focuses on the outside view of an object and so serves to separate an object’s essential behavior from its implementation. �Deciding on the right set of abstractions for a given domain is the central problem in object-oriented design.
Abstraction �Abstraction or separation of behavior / implementation can be achieved by applying: �Principle of least commitment: the interface of an object provides its essential behavior, and nothing more �Principle of least astonishment: an abstraction captures the entire behavior of some object, no more and no less, and offers no surprises or side effects that go beyond the scope of the abstraction
Abstract Data Type (ADT) �An ADT is a mathematical model of a data structure that specifies the type of data stored, the operations supported on them and the type of parameters of the operations. �Specifies what each operation does, but not how it does it
Encapsulation �Encapsulation hides the details of the implementation of an object Typically, the structure of an object is hidden, as well as the implementation of its methods. Encapsulation is the process of compartmentalizing the elements of an abstraction that constitute its structure and behavior; Encapsulation serves to separate the contractual interface of an abstraction and its implementation.
Encapsulation
Encapsulation � Encapsulation is most often achieved through information hiding (not just data hiding), which is the process of hiding all the secrets of an object that do not contribute to its essential characteristics
Data/Information Hiding Access House X Modify. X () Modify X Private data – hidden from others Function to safeguard the private data
Data Hiding �". . . the purpose of hiding is to make inaccessible certain details that should not affect other parts of a system. “ [Ross et al, 1975]
Data Hiding �Data must be hidden/ private �Read access through read() functions �Write access through write() functions �For each data, Allow both read and write Allow read only Allow write only No access
Encapsulation / Data Hiding void modify. X (int new. Val) { if (new. Val > 100) or (new. Val < 0) { return error; } else X = new. Val } void read. X() { return X; }
Abstraction & Encapsulation � Complementary concepts: The abstraction of an object should precede the decisions about its implementation. Once an implementation is selected, it should be treated as a secret of the abstraction and hidden from most clients i. e. encapsulated � “For abstraction to work, implementations must be encapsulated � Abstraction: focuses on the observable behavior of an object � Encapsulation: focuses on the implementation that gives rise to this behavior
Anatomy of a Class • Realization of an ADT • State /fields /data members Public Interface PRIVATE Data • Behavior /methods /member functions • Public Interface: signatures (names, return types, argument types) of a class’s public member functions, only part of the class that can be accessed by a user of the class PUBLIC Read/ Write Functions Constructors/ Destructors Private Functions ADT Functions Pop(), Insert ()
Class • It defines the data being stored and the operations supported by the objects that are instances of the class • Every class must have two parts: • • an interface – what? – Abstraction an implementation – how? – Encapsulation
Class, Abstraction & Encapsulation Abstraction Encapsulation �External Interface The interface of a class captures only its outside view, encompassing abstraction of the behavior common to all instances of the class. �Internal Implementation The implementation of a class comprises the representation of the abstraction as well as the mechanisms that achieve the desired behavior.
Class, Abstraction & Encapsulation Abstraction �Exposes Generic / Generalized Features The interface of a class is the one place where we assert all of the assumptions that a client may make about any instances of the class �Hides implementation details The implementation encapsulates details about which no client may make assumptions. In C++ a Class embodies both abstraction and encapsulation Please read: http: //www. tonymarston. co. uk/php-mysql/abstraction. txt
Examples Point Product class Point { public: class Product { public: Point (double xval, double yval); void move(double dx, double dy); double get_x() const; double get_y() const; Product(); void read(); bool is_better_than(Product b) const; void print() const; private: double x; double y; private: string name; double price; int score; }; };
Objects � Object Instantiation of a class � Initialization of Objects Constructors Called automatically every time an object is created, ensures proper initialization Overcome the problem of improper initialization in procedural languages � Resource De-allocation Destructors Ensures de-allocation of resources before the object dies, or goes out of scope Overcome memory leaks etc. in procedural languages
Objects �Life-cycle of an Object Born Healthy � Properly Lives Safely � Using initialized by use of constructors read/write functions, ensure data integrity Dies Cleanly � Using destructors
References �[Lafore] Chapter 1 �[Booch et al] Chapters 1 & 2 �[Deital & Deital] Chapter 3 �[Horstmann & Budd] Chapter 5 �http: //www. tonymarston. co. uk/php- mysql/abstraction. txt
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