Introduction to Object-Oriented Concepts in Computer Science

1. CPS120: Introduction to Computer Science Object-Oriented Concepts

2. The Procedural Paradigm • The functions and algorithms are the focus, with data viewed as something for the functions to manipulate

3. Object-Oriented Paradigm • Data should be placed inside the objects and that these objects should communicate with each other in the form of messages

4. Designing a Class • Think in an object-oriented way • E.g. an answering machine encapsulates the functions of an answering machine with the data (messages). • The buttons are the equivalent of sending messages to the machine

5. Functionality of Object-Oriented Languages • Encapsulation • Inheritance • Polymorphism

6. Encapsulation • Encapsulation is a language feature that enforces information hiding • A class is a language construct that is a pattern for an object and provides a mechanism for encapsulating the properties and actions of the object class • We instantiate the class • Private and public are called access modifiers

7. Inheritance • Inheritance fosters reuse by allowing an application to take an already-tested class and derive a class from it that inherits the properties the application needs • Polymorphism: the ability of a language to have duplicate method names in an inheritance hierarchy and to apply the method that is appropriate for the object to which the method is applied

8. Polymorphism • The ability of a language to have duplicate method names in an inheritance hierarchy and to apply the method that is most appropriate for the object which the method is applied

9. Object-Oriented Design • A problem-solving methodology that produces a solution to a problem in terms of self-contained entities called objects • An object is a thing or entity that makes sense within the context of the problem • For example, a student

10. Object-Oriented Design • A group of similar objects is described by an object class, or class • A class contains fields that represent the properties and behaviors of the class • A field can contain data value(s) and/or methods (subprograms) • A method is a named algorithm that manipulates the data values in the object

11. OOP • Object-oriented programming (OOP) is the process of developing programs using the object-oriented paradigm

12. OOP Advantages: Reusability • Reusability is a major benefit of object-oriented programming

13. OOP Advantages: Containment • Containment is a term used to describe an object that contains one or more objects as members (Passes the 'has-a' rule)

14. OOP Advantages: Inheritance • Inheritance is the term used to describe an object that inherits properties from another object (Passes the 'is-a' rule) • The class from which an object inherits properties is called a parent class or base class • The class that inherits the properties is called a child class or derived class

15. Classes • The definition of an object is know as a class • It is similar to using basic data structures in C++ • When you declare an object, you are said to have instantiated it (given it instances) • Objects are members of a class • Paul Millis, George Bush and George Washington being members of the human being class • The design of a class is as important as its implementation

16. Relationships Between Classes • Containment • “part-of” • An address class may be part of the definition of a student class • Inheritance • Classes can inherit data and behavior from other classes • “is-a”

17. Including Classes in C++ • For classes, the #include directive uses different punctuation for header (.h) files • Quotation marks are used when the header file is a source file in the same location as the program source code • Angle brackets are used when the header file is one of the compiler's pre-compiled library functions

18. Using Header Files for Classes • Header files normally contain declarations of variables, functions and classes, but not implementations of the functions and classes

19. Defining a Class • Functions and variables that are prototyped and declared in a class definition are called members

20. Public vs Private • Private: Cannot be accessed outside the object • Public: Can have access to all the variables and functions public: // constructors circle(); // default constructor circle(const circle &); // copy constructor // member functions void SetRadius(float); double Area(); private: // data float radius;

21. Constructors • Allow all data encapsulated within an object to be initialized to preset values so that errors can be avoided

22. Member Functions • Provide a way for a programmer to pass data to and get data from an object • Implemented like a normal C++ function • Except -- The class name and the scope-resolution operator (: :) precede the function name • circle : : circle() // default constructor