Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Starting Out with Programming Logic & Design Second Edition by Tony Gaddis Chapter 14: Object-Oriented Programming

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 14-2 Chapter Topics 14.1 Procedural and Object-Oriented Programming 14.2 Classes 14.3 Using the Unified Modeling Language to Design Classes 14.4 Inheritance 14.5 Polymorphism

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Procedural and Object-Oriented Programming Procedural Programming An early method of coding where programs are centered on the procedures or actions that take place in a program A procedure is simply a module As program get larger and more complex, this method leads to problems The procedures in a program written in a procedural language are in a preset order. The program moves from procedure to procedure typically without user interaction. Object Oriented Programming A newer method of coding where programs are centered on creating objects An object is a software entity that contains both data and procedures The data in a object is known as the object’s fields (variables, arrays…) The procedures that are performed are called methods

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Procedural and Object-Oriented Programming Object Oriented Programming (OOP) addresses the procedural problem of code/data separation by using two methods –Encapsulation – refers to the combining of data and code into a single object –Data hiding – refers to an object’s ability to hide its data from code that is outside the object Another OOP benefit is Object Reusability –For example, an object that renders 3D images can be used in many different programs

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Classes A class is code that specifies the fields and methods for a particular type of object –A class is coded and contains methods and fields Think of it like a blueprint, such as a blueprint for a house It’s a detailed description –An object is then created from the class It is an instance of a class Think of it as the actual house (For example, a button on a form belongs to a ‘button class’ in the particular language used to create the button. Every time a button is needed by the programmer, an ‘instance of the button is created’)

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Classes Creating a class Class ClassName Field declarations and method declarations End Class –The first line starts with Class, followed by the name of the class The programmer names the class following the same rules as naming variables –The field declarations (variables) and methods are defined within the class (Note: Take a look a Visual Basic form: see a class with its properties and methods. Ex. Text Box -> focus method)

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Classes Access specifiers –Private allows class members to be hidden from code outside the class –Public allows for all parts of the code to access the class members –It is common practice to make all fields private and to provide access only to those field through methods –Therefore, the methods should be public

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Classes Continued…

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Classes

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Classes Inside Class Listing 14-3 –The field are defined as private to ensure data hiding –The methods are public so they can be accessed by main –When the set modules are called, a String is passed into the method as an argument and that value is set to the private field –When the get modules are called, they simply return the value of the private field

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Classes

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Classes

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Classes Inside Program 14-1 –An variable is created myPhone –myPhone is then used with the keyword New to create the object in memory –Values are then stored in the object’s field by calling the class methods Call myPhone.setManufacturer(“Motorola”) –Values are then displayed by calling the class methods Display “The manufacturer is “, myPhone.getManufacturer( ) –The dot notation is used to associate an object with a member of the class

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Classes Constructor is a method that is automatically called when an object is created –The purpose is to initialize an object’s fields with starting values –A programmer can write their own constructor to initialize fields –Or they can use the default constructor that is available with most programming languages

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Using the Unified Modeling Language to Design Classes The Unified Modeling Language (UML) is a standard way of drawing diagrams that describe object-oriented systems –Contains a set of standard diagrams for graphically depicting OO systems Figure General layout of a UML diagram for a class

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Using the Unified Modeling Language to Design Classes Data type, method parameter, and access specification notation is also added to a UML diagram –The data type specifies the data type of the field or the data type of the method –The method parameter specifies the parameter variables and their data types –The access specification indicates a + for public or a – for private

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Using the Unified Modeling Language to Design Classes Figure UML diagram for the CellPhone class with access specification notation

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Inheritance Inheritance allows a new class to extend an existing class, whereas the new class inherits the members of the class it extends –The superclass is the base class –The subclass(es) is the derived class Figure Bumblebees and grasshoppers are specialized versions of an insect

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Polymorphism Polymorphism allows you to create methods with the same name in different classes (that are related through inheritance –The programmer has the ability to call the correct method depending on the type of object that is used to call it –Polymorphism refers to an object’s ability to take different forms

Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley #Program 14 ‐ 1 class CellPhone: def set_manufacturer(self, manufact): self.__manufacturer = manufact def set_model_number(self, model): self.__model_number = model def set_retail_price(self, retail): self.__retail_price = retail def get_manufacturer(self): return self.__manufacturer def get_model_number(self): return self.__model_number def get_retail_price(self): return self.__retail_price def main(): # Create a CellPhone object. The phone # variable will reference the object. phone = CellPhone() # Store values in the object's fields. phone.set_manufacturer("Motorola") phone.set_model_number("M1000") phone.set_retail_price(199.99) # Display the values stored in the fields. print 'The manufacturer is', phone.get_manufacturer() print 'The model number is', phone.get_model_number() print 'The retail price is', phone.get_retail_price() # Call the main function. main()