Object Oriented Programming Development By: Marc Conrad University of Luton Email: [email protected] Room: D104 1 What are we doing today? Introduction of: the lecturer Objects Basic Terminology C++ the module 2 What is Object Oriented Programming? An object is like a black box. The internal details are hidden. Identifying objects and assigning responsibilities to these objects. Objects communicate to other objects by sending messages. Messages are received by the methods of an object 3 What is an object? Tangible Things Roles Incidents Interactions Specifications as a car, printer, ... as employee, boss, ... as flight, overflow, ... as contract, sale, ... as colour, shape, … 4 So, what are objects? an object represents an individual, identifiable item, unit, or entity, either real or abstract, with a well-defined role in the problem domain. Or An "object" is anything to which a concept applies. Etc. 5 Why do we care about objects? Modularity - large software projects can be split up in smaller pieces. Reuseability - Programs can be assembled from pre-written software components. Extensibility - New software components can be written or developed from existing ones. 6 Example: The Person class #include<string> #include<iostream> class Person{ private char name[20]; data int yearOfBirth; public: void displayDetails() { cout << name << " born in " << yearOfBirth << endl; public } processes //... }; The two parts of an object Object = Data + Methods or to say the same differently: An object has the responsibility to know and the responsibility to do. = + 8 Basic Terminology Abstraction is the representation of the essential features of an object. These are �encapsulated’ into an abstract data type. Encapsulation is the practice of including in an object everything it needs hidden from other objects. The internal state is usually not accessible by other objects. 9 Basic Terminology: Inheritance Inheritance means that one class inherits the characteristics of another class. This is also called a “is a” relationship: A car is a vehicle A dog is an animal A teacher is a person 10 Basic Terminology: Polymorphism Polymorphism means “having many forms”. It allows different objects to respond to the same message in different ways, the response specific to the type of the object. E.g. the message displayDetails() of the Person class should give different results when send to a Student object (e.g. the enrolment number). 11 Basic Terminology: Aggregation Aggregation describes a “has a” relationship. One object is a part of another object. A car has wheels. We distinguish between composite aggregation (the composite “owns” the part) and shared aggregation (the part is shared by more then one composite). 12 Basic Terminology: Behaviour and Messages The most important aspect of an object is its behaviour (the things it can do). A behaviour is initiated by sending a message to the object (usually by calling a method). 13 The two steps of Object Oriented Programming Making Classes: Creating, extending or reusing abstract data types. Making Objects interact: Creating objects from abstract data types and defining their relationships. 14 Historical Notes C++ owes most to C. Other ancestors are Simula67 C++ 1987 and Algol68. First versions of C++ in 1980 under the name “C with classes”. Since 1983 the name C++ is used. 1990: ANSI/ISO 9899 defines a standard for C 1998: ISO/IEC 14882 specifies the 15 standard for C++ C++ and C C is a subset of C++. Advantages: Existing C libraries can be used, efficient code can be generated. But: C++ has the same caveats and problems as C (e.g. pointer arithmetic,…). C++ can be used both as a low level and as a high level language. e h t n o s u c . o s f t c e e p W s a l e v e l 16 high C++ and Java Java is a full object oriented language, all code has to go into classes. C++ - in contrast - is a hybrid language, capable both of functional and object oriented programming. So, C++ is more powerful but also more difficult to handle than Java. 17 Module Outline Introduction The non object oriented basics Classes Design Approaches Testing Inheritance Aggregation Polymorphism Multifile Development 18 Assessment Details 50% in course and 50% exam. For more details for the in course assignment see separate handout. 19 Books Teach Yourself C++ in 10 minutes, J. Liberty, SAMS 1999. C++ - How to program, Deitel & Deitel, Prentice Hall, 2001. Object Oriented Programming with C++, David Parson, Letts Educational, London 1997. 20 Websites A C++ online tutorial: http://www.cplusplus.com/doc/tutorial/ The C++ FAQ: http://www.parashift.com/c++-faq-lite The homepage of Bjarne Stroustrup, the inventor of C++: http://www.research.att.com/~bs ! e r o m y n a m , y n 21 a m d An
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