Summary Programming Logic and Design Ch 10

Chapter 10
The principles of object-oriented programming
 Object-oriented programming (OOP)
 A programming model that focuses on an application’s components and data and the
methods to manipulate them
 Uses all of the familiar concepts from modular procedural programming
 Variables, methods, passing arguments
 Sequence, selection, and looping structures
 But involves a different way of thinking
 Important features of object-oriented languages
 Classes
 Objects
 Polymorphism
 Inheritance
 Encapsulation


Classes
 Class
 Describes a group or collection of objects with common attributes
 Object - One instance of a class
 Sometimes called one instantiation of a class
 When a program creates an object, it instantiates the object
 Example
 Class name: dog
 Attributes: name, age, hasShots
 Methods: changeName, updateShots
 Attributes
 Characteristics that define an object as part of a class
 Example
 Automobile’s attributes: make, model, year, and purchase price
 Methods
 Actions that alter, use, or retrieve the attributes
 Example
 Methods for changing an automobile’s running status, gear, speed, and cleanliness
 Think in an object-oriented manner
 Everything is an object
 Every object is a member of a class
 Is-a relationship

,  “My oak desk with the scratch on top is a Desk”
 Class reusability
 Class’s instance variables
 Data components of a class that belong to every instantiated object
 Often called fields
 State
 A set of all the values or contents of a class object’s instance variables
 Every object that is an instance of a class possesses the same methods
 Create classes from which objects will be instantiated
 Class client or class user
 A program or class that instantiates objects of another prewritten class


Polymorphism
 The world is full of objects
 A door is an object that needs to be open or closed
 But an “open” procedure works differently on different objects
 Open a door
 Open a drawer
 Open a bank account
 Open a file
 Open your eyes
 One “open” procedure can open anything if it gets the correct arguments


Inheritance
 Inheritance
 The process of acquiring the traits of one’s predecessors
 Example
 A door with a stained-glass window inherits all the attributes (doorknob, hinges) and
methods (open and close) of a door
 Once you create an object
 Develop new objects that possess all the traits of the original object
 Plus, new traits


Encapsulation
 Encapsulation
 The process of combining all of an object’s attributes and methods into a single package
 Information hiding (also called data hiding)
 Other classes should not alter an object’s attributes
 Outside classes should only be allowed to make a request that an attribute be altered
 It is up to the class’s methods to determine whether the request is appropriate