Learning Object-Oriented Programming
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About this ebook
- Write reusable code that defines and makes objects interact with one another
- Discover the differences in inheritance and polymorphism in Python, JavaScript, and C#
- Capture objects from real-world elements and create object-oriented code that represents them
If you're a Python, JavaScript, or C# developer and want to learn the basics of object-oriented programming with real-world examples, then this book is for you.
Gastón C. Hillar
Gaston C. Hillar has been working with computers since he was eight. He began programming with the legendary Texas TI-99/4A and Commodore 64 home computers in the early 80s. He has a Bachelor degree in Computer Science, graduated with honors, and an MBA (Master in Business Administration), graduated with an outstanding thesis. He worked as developer, architect, and project manager for many companies in Buenos Aires, Argentina. Now, he is an independent IT consultant and a freelance author always looking for new adventures around the world. He also works with electronics (he is an electronics technician). He is always researching about new technologies and writing about them. He owns an IT and electronics laboratory with many servers, monitors, and measuring instruments. Gaston write the C# 2008 and 2005 Threaded Programming: Beginner's Guide also published by Packt. He is also the author of more than 40 books in Spanish about computer science, modern hardware, programming, systems development, software architecture, business applications, balanced scorecard applications, IT project management, the Internet, and electronics. He contributes to Dr. Dobb's Go Parallel programming portal http://www.ddj.com/go-parallel/ and he is a guest blogger at Intel Software Network http://software.intel.com He usually writes articles for Spanish magazines Mundo Linux, Solo Programadores and Resistor.
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Learning Object-Oriented Programming - Gastón C. Hillar
Table of Contents
Learning Object-Oriented Programming
Credits
About the Author
Acknowledgments
About the Reviewers
www.PacktPub.com
Support files, eBooks, discount offers, and more
Why subscribe?
Free access for Packt account holders
Preface
What this book covers
What you need for this book
Who this book is for
Conventions
Reader feedback
Customer support
Downloading the example code
Errata
Piracy
eBooks, discount offers, and more
Questions
1. Objects Everywhere
Recognizing objects from nouns
Generating blueprints for objects
Recognizing attributes/fields
Recognizing actions from verbs – methods
Organizing the blueprints – classes
Object-oriented approaches in Python, JavaScript, and C#
Summary
2. Classes and Instances
Understanding classes and instances
Understanding constructors and destructors
Declaring classes in Python
Customizing constructors in Python
Customizing destructors in Python
Creating instances of classes in Python
Declaring classes in C#
Customizing constructors in C#
Customizing destructors in C#
Creating instances of classes in C#
Understanding that functions are objects in JavaScript
Working with constructor functions in JavaScript
Creating instances in JavaScript
Summary
3. Encapsulation of Data
Understanding the different members of a class
Protecting and hiding data
Working with properties
Understanding the difference between mutability and immutability
Encapsulating data in Python
Adding attributes to a class
Hiding data in Python using prefixes
Using property getters and setters in Python
Using methods to add behaviors to classes in Python
Encapsulating data in C#
Adding fields to a class
Using access modifiers
Using property getters and setters in C#
Working with auto-implemented properties
Using methods to add behaviors to classes in C#
Encapsulating data in JavaScript
Adding properties to a constructor function
Hiding data in JavaScript with local variables
Using property getters and setters in JavaScript
Using methods to add behaviors to constructor functions
Summary
4. Inheritance and Specialization
Using classes to abstract behavior
Understanding inheritance
Understanding method overloading and overriding
Understanding operator overloading
Taking advantage of polymorphism
Working with simple inheritance in Python
Creating classes that specialize behavior in Python
Using simple inheritance in Python
Overriding methods in Python
Overloading operators in Python
Understanding polymorphism in Python
Working with simple inheritance in C#
Creating classes that specialize behavior in C#
Using simple inheritance in C#
Overloading and overriding methods in C#
Overloading operators in C#
Understanding polymorphism in C#
Working with the prototype-based inheritance in JavaScript
Creating objects that specialize behavior in JavaScript
Using the prototype-based inheritance in JavaScript
Overriding methods in JavaScript
Overloading operators in JavaScript
Understanding polymorphism in JavaScript
Summary
5. Interfaces, Multiple Inheritance, and Composition
Understanding the requirement to work with multiple base classes
Working with multiple inheritance in Python
Declaring base classes for multiple inheritance
Declaring classes that override methods
Declaring a class with multiple base classes
Working with instances of classes that use multiple inheritance
Working with abstract base classes
Interfaces and multiple inheritance in C#
Declaring interfaces
Declaring classes that implement interfaces
Working with multiple inheritance
Working with methods that receive interfaces as arguments
Working with composition in JavaScript
Declaring base constructor functions for composition
Declaring constructor functions that use composition
Working with an object composed of many objects
Working with instances composed of many objects
Summary
6. Duck Typing and Generics
Understanding parametric polymorphism and duck typing
Working with duck typing in Python
Declaring a base class that defines the generic behavior
Declaring subclasses for duck typing
Declaring a class that works with duck typing
Using a generic class for multiple types
Working with duck typing in mind
Working with generics in C#
Declaring an interface to be used as a constraint
Declaring an abstract base class that implements two interfaces
Declaring subclasses of an abstract base class
Declaring a class that works with a constrained generic type
Using a generic class for multiple types
Declaring a class that works with two constrained generic types
Using a generic class with two generic type parameters
Working with duck typing in JavaScript
Declaring a constructor function that defines the generic behavior
Working with the prototype chain and duck typing
Declaring methods that work with duck typing
Using generic methods for multiple objects
Working with duck typing in mind
Summary
7. Organization of Object-Oriented Code
Thinking about the best ways to organize code
Organizing object-oriented code in Python
Working with source files organized in folders
Importing modules
Working with module hierarchies
Organizing object-oriented code in C#
Working with folders
Using namespaces
Working with namespace hierarchies in C#
Organizing object-oriented code in JavaScript
Working with objects to organize code
Declaring constructor functions within objects
Working with nested objects that organize code
Summary
8. Taking Full Advantage of Object-Oriented Programming
Putting together all the pieces of the object-oriented puzzle
Refactoring existing code in Python
Refactoring existing code in C#
Refactoring existing code in JavaScript
Summary
Index
Learning Object-Oriented Programming
Learning Object-Oriented Programming
Copyright © 2015 Packt Publishing
All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.
Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.
Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.
First published: July 2015
Production reference: 1100715
Published by Packt Publishing Ltd.
Livery Place
35 Livery Street
Birmingham B3 2PB, UK.
ISBN 978-1-78528-963-7
www.packtpub.com
Credits
Author
Gastón C. Hillar
Reviewers
Róman Joost
Hugo Solis
Commissioning Editor
Sarah Croufton
Acquisition Editor
Nadeem Bagban
Content Development Editor
Divij Kotian
Technical Editor
Parag Topre
Copy Editor
Relin Hedly
Project Coordinator
Nikhil Nair
Proofreader
Safis Editing
Indexer
Monica Ajmera Mehta
Graphics
Disha Haria
Production Coordinator
Arvindkumar Gupta
Cover Work
Arvindkumar Gupta
About the Author
Gastón C. Hillar is an Italian and has been working with computers since he was 8 years old. In the early 80s, he began programming with the legendary Texas TI-99/4A and Commodore 64 home computers. Gaston has a bachelor's degree in computer science and graduated with honors. He also holds an MBA, in which he graduated with an outstanding thesis. At present, Gaston is an independent IT consultant and a freelance author who is always looking for new adventures around the world.
He has been a senior contributing editor at Dr. Dobb's and has written more than a hundred articles on software development topics. Gatson was also a former Microsoft MVP in technical computing. He has received the prestigious Intel® Black Belt Software Developer award seven times.
He is a guest blogger at Intel® Software Network (http://software.intel.com). You can reach him at
He lives with his wife, Vanesa, and his two sons, Kevin and Brandon.
Acknowledgments
At the time of writing this book, I was fortunate to work with an excellent team at Packt Publishing. Their contributions vastly improved the presentation of this book. James Jones gave me a brilliant idea that led me to jump into the exciting project of teaching object-oriented programming in three popular, yet heterogeneous, programming languages. Divij Kotian helped me realize my vision for this book and provided many sensible suggestions regarding the text, format, and flow of the book, which is quite noteworthy. I would like to thank my technical reviewers and proofreaders for their thorough reviews and insightful comments. I was able to incorporate some of the knowledge and wisdom that they have gained in their many years in the software development industry. This book was possible because of their valuable feedback.
The entire process of writing a book requires a huge number of lonely hours. I couldn't have written an entire book without dedicating some time to play soccer with my sons, Kevin and Brandon, and my nephew, Nicolas. Of course, I never won a match.
About the Reviewers
Róman Joost first learned about open source software in 1997. He has contributed to multiple open source projects in his professional career. Roman is currently working at Red Hat in Brisbane, Australia. In his leisure time, he enjoys photography, spending time with his family, and digital painting with GIMP.
Hugo Solis is an assistant professor in the physics department at the University of Costa Rica. His current research interests include computational cosmology, complexity, and the influence of hydrogen on material properties. Hugo has vast experience in languages, including C, C++, and Python for scientific programming and visualization. He is a member of the Free Software Foundation and has contributed code to some free software projects. Hugo has contributed to Mastering Object-oriented Python and Kivy: Interactive Applications in Python as a technical reviewer and is the author of Kivy Cookbook, Packt Publishing. He is currently in charge of the IFT, a Costa Rican scientific nonprofit organization for the multidisciplinary practice of physics (http://iftucr.org).
I'd like to thank my beloved mother, Katty Sanchez, for her support and vanguard thoughts.
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To my sons, Kevin and Brandon, and my wife, Vanesa
Preface
Object-oriented programming, also known as OOP, is a required skill in absolutely any modern software developer job. It makes a lot of sense because object-oriented programming allows you to maximize code reuse and minimize the maintenance costs. However, learning object-oriented programming is challenging because it includes too many abstract concepts that require real-life examples to make it easy to understand. In addition, object-oriented code that doesn't follow best practices can easily become a maintenance nightmare.
Nowadays, you need to work with more than one programming language at the same time to develop applications. For example, a modern Internet of Things project may require the Python code running on a board and a combination of C#, JavaScript, and HTML code to develop both the web and mobile apps that allow users to control the Internet of Things device. Thus, learning object-oriented programming for a single programming language is usually not enough.
This book allows you to develop high-quality reusable object-oriented code in Python, JavaScript, and C#. You will learn the object-oriented programming principles and how they are or will be used in each of the three covered programming languages. You will also learn how to capture objects from real-world elements and create object-oriented code that represents them. This book will help you understand the different approaches of Python, JavaScript, and C# toward object-oriented code. You will maximize code reuse in the three programming languages and reduce maintenance costs. Your code will become easy to understand and it will work with representations of real-life elements.
What this book covers
Chapter 1, Objects Everywhere, covers the principles of object-oriented paradigms and some of the differences in the approaches toward object-oriented code in each of the three covered programming languages: Python, JavaScript, and C#. You will understand how real-world objects can become part of fundamental elements in the code.
Chapter 2, Classes and Instances, tells you how to generate blueprints in order to create objects. You will understand the difference between classes, prototypes, and instances in object-oriented programming.
Chapter 3, Encapsulation of Data, teaches you how to organize data in the blueprints that generate objects. You will understand the different members of a class, learn the difference between mutability and immutability, and customize methods and fields to protect them against undesired access.
Chapter 4, Inheritance and Specialization, explores how to create a hierarchy of blueprints that generate objects. We will take advantage of inheritance and many related features to specialize behavior.
Chapter 5, Interfaces, Multiple Inheritance, and Composition, works with more complex scenarios in which we have to use instances that belong to more than one blueprint. We will use the different features included in each of the three covered programming languages to code an application that requires the combination of multiple blueprints in a single instance.
Chapter 6, Duck Typing and Generics, covers how to maximize code reuse by writing code capable of working with objects of different types. In this chapter, you will learn parametric polymorphism, generics, and duck typing.
Chapter 7, Organization of Object-Oriented Code, provides information on how to write code for a complex application that requires dozens of classes, interfaces, and constructor functions according to the programing language that you use. It will help you understand the importance of organizing object-oriented code and think about the best solution to organize object-oriented code.
Chapter 8, Taking Full Advantage of Object-Oriented Programming, talks about how to refactor existing code to take advantage of all the object-oriented programming techniques that you learned so far. The difference between writing object-oriented code from scratch and refactoring existing code is explained in this chapter. It will also help you prepare object-oriented code for future requirements.
What you need for this book
You will need a computer with at least an Intel Core i3 CPU or equivalent with 4 GB RAM, running on Windows 7 or a higher version, Mac OS X Mountain Lion or a higher version, or any Linux version that is capable of running Python 3.4, and a browser with JavaScript support.
You will need Python 3.4.3 installed on your computer. You can work with your favorite editor or use any Python IDE that is compatible with the mentioned Python version.
In order to work with the C# examples, you will need Visual Studio 2015 or 2013. You can use the free Express editions to run all the examples. If you aren't working on Windows, you can use Xamarin Studio 5.5 or higher.
In order to work with the JavaScript examples, you will need web browsers such as Chrome 40.x or higher, Firefox 37.x or higher, Safari 8.x or higher, Internet Explorer 10 or higher that provides a JavaScript console.
Who this book is for
If you're a Python, JavaScript, or C# developer and want to learn the basics of object-oriented programming with real-world examples, this book is for you.
Conventions
In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.
Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: We can use a rectangle class as a blueprint to generate the four different rectangle instances.
A block of code is set as follows:
function calculateArea(width, height) {
return new Rectangle(width, height).calculateArea();
}
calculateArea(143, 187);
When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:
function Mammal() {} Mammal.prototype = new Animal(); Mammal.prototype.constructor = Mammal;
Mammal.prototype.isPregnant = false;
Mammal.prototype.pairsOfEyes = 1;
Any command-line input or output is written as follows:
Rectangle {width: 293, height: 117} Rectangle {width: 293, height: 137}
New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: The following line prints
System.Object as a result in the Immediate Window in the IDE.
Note
Warnings or important notes appear in a box like this.
Tip
Tips and tricks appear like this.
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Chapter 1. Objects Everywhere
Objects are everywhere, and therefore, it is very important to recognize elements, known as objects, from real-world situations. It is also important to understand how they can easily be translated into object-oriented code. In this chapter, you will learn the principles of object-oriented paradigms and some of the differences in the approaches towards object-oriented code in each of the three programming languages: Python, JavaScript, and C#. In this chapter, we will:
Understand how real-world objects can become a part of fundamental elements in the code
Recognize objects from nouns
Generate blueprints for objects and understand classes
Recognize attributes to generate fields
Recognize actions from verbs to generate methods
Work with UML diagrams and translate them into object-oriented code
Organize blueprints to generate different classes
Identify the object-oriented approaches in Python, JavaScript, and C#
Recognizing objects from nouns
Let's imagine, we have to develop a new simple application, and we receive a description with the requirements. The application must allow users to calculate the areas and perimeters of squares, rectangles, circles, and ellipses.
It is indeed a very simple application, and you can start writing code in Python, JavaScript, and C#. You can create four functions that calculate the areas of the shapes mentioned earlier. Moreover, you can create four additional functions that calculate the perimeters for them. For example, the following seven functions would do the job:
calculateSquareArea: This receives the parameters of the square and returns the value of the calculated area for the shape
calculateRectangleArea: This receives the parameters of the rectangle and returns the value of the calculated area for the shape
calculateCircleArea: This receives the parameters of the