Features and Benefits
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Revision of a clear, concise and accessible introduction to object-oriented programming concepts
* Helps working programmers learn to think in terms of object-oriented technologies and understand object-oriented applications before coding starts
* Author is an expert trainer and teacher
* No bias to any one language or platform - examples are drawn from Java, VB.NET and C#, but are applicable to any object-oriented language, from C++ to Java to Ruby to .NET
Table of Contents
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Introduction 1
1 Introduction to Object-Oriented Concepts 5
Procedural Versus OO Programming 6
Moving from Procedural to Object-Oriented Development 9
Procedural Programming 9
OO Programming 10
What Exactly Is an Object? 10
Object Data 10
Object Behaviors 11
What Exactly Is a Class? 14
Classes Are Object Templates 15
Attributes 17
Methods 17
Messages 17
Using UML to Model a Class Diagram 18
Encapsulation and Data Hiding 19
Interfaces 19
Implementations 20
A Real-World Example of the Interface/Implementation Paradigm 20
A Model of the Interface/Implementation Paradigm 21
Inheritance 22
Superclasses and Subclasses 23
Abstraction 23
Is-a Relationships 25
Polymorphism 25
Composition 28
Abstraction 29
Has-a Relationships 29
Conclusion 29
Example Code Used in This Chapter 30
2 How to Think in Terms of Objects 37
Knowing the Difference Between the Interface and the Implementation 38
The Interface 40
The Implementation 40
An Interface/Implementation Example 41
Using Abstract Thinking When Designing Interfaces 45
Giving the User the Minimal Interface Possible 47
Determining the Users 48
Object Behavior 48
Environmental Constraints 48
Identifying the Public Interfaces 49
Identifying the Implementation 50
Conclusion 50
References 51
3 Advanced Object-Oriented Concepts 53
Constructors 53
The Default Constructor 54
When Is a Constructor Called? 54
What's Inside a Constructor? 54
The Default Constructor 54
Using Multiple Constructors 55
The Design of Constructors 59
Error Handling 60
Ignoring the Problem 60
Checking for Problems and Aborting the Application 60
Checking for Problems and Attempting to Recover 61
Throwing an Exception 61
The Concept of Scope 63
Local Attributes 64
Object Attributes 65
Class Attributes 67
Operator Overloading 68
Multiple Inheritance 69
Object Operations 70
Conclusion 71
References 71
Example Code Used in This Chapter 72
4 The Anatomy of a Class 75
The Name of the Class 75
Comments 77
Attributes 77
Constructors 79
Accessors 80
Public Interface Methods 83
Private Implementation Methods 83
Conclusion 84
References 84
Example Code Used in This Chapter 84
5 Class Design Guidelines 87
Modeling Real World Systems 87
Identifying the Public Interfaces 88
The Minimum Public Interface 88
Hiding the Implementation 89
Designing Robust Constructors (and Perhaps Destructors) 89
Designing Error Handling into a Class 90
Documenting a Class and Using Comments 91
Building Objects with the Intent to Cooperate 91
Designing with Reuse in Mind 91
Documenting a Class and Using Comments 91
Designing with Extensibility in Mind 92
Making Names Descriptive 92
Abstracting Out Nonportable Code 93
Providing a Way to Copy and Compare Objects 93
Keeping the Scope as Small as Possible 94
A Class Should Be Responsible for Itself 95
Designing with Maintainability in Mind 96
Using Iteration 97
Testing the Interface 97
Using Object Persistence 99
Serializing and Marshaling Objects 100
Conclusion 100
References 101
Example Code Used in This Chapter 101
6 Designing with Objects 103
Design Guidelines 103
Performing the Proper Analysis 107
Developing a Statement of Work 107
Gathering the Requirements 107
Developing a Prototype of the User Interface 108
Identifying the Classes 108
Determining the Responsibilities of Each Class 108
Determining How the Classes Collaborate with Each Other 109
Creating a Class Model to Describe the System 109
Case Study: A Blackjack Example 109
Using CRC Cards 111
Identifying the Blackjack Classes 112
Identifying the Classes' Responsibilities 115
UML Use-Cases: Identifying the Collaborations 120
First Pass at CRC Cards 124
UML Class Diagrams: The Object Model 126
Prototyping the User Interface 127
Conclusion 127
References 128
7 Mastering Inheritance and Composition 129
Reusing Objects 129
Inheritance 130
Generalization and Specialization 133
Design Decisions 134
Composition 135
Representing Composition with UML 136
Why Encapsulation Is Fundamental to OO 138
How Inheritance Weakens Encapsulation 139
A Detailed Example of Polymorphism 141
Object Responsibility 141
Conclusion 145
References 146
Example Code Used in This Chapter 146
8 Frameworks and Reuse: Designing with Interfaces and Abstract Classes 151
Code: To Reuse or Not to Reuse? 151
What Is a Framework? 152
What Is a Contract? 153
Abstract Classes 154
Interfaces 157
Tying It All Together 159
The Compiler Proof 161
Making a Contract 162
System Plug-in-Points 165
An E-Business Example 165
An E-Business Problem 165
The Non-Reuse Approach 166
An E-Business Solution 168
The UML Object Model 168
Conclusion 173
References 173
Example Code Used in This Chapter 173
9 Building Objects 179
Composition Relationships 179
Building in Phases 181
Types of Composition 183
Aggregations 183
Associations 184
Using Associations and Aggregations Together 185
Avoiding Dependencies 186
Cardinality 186
Multiple Object Associations 189
Optional Associations 190
Tying It All Together: An Example 191
Conclusion 192
References 192
10 Creating Object Models with UML 193
What Is UML? 193
The Structure of a Class Diagram 194
Attributes and Methods 196
Attributes 196
Methods 197
Access Designations 197
Inheritance 198
Interfaces 200
Composition 201
Aggregations 201
Associations 201
Cardinality 204
Conclusion 205
References 205
11 Objects and Portable Data: XML 207
Portable Data 207
The Extensible Markup Language (XML) 209
XML Versus HTML 209
XML and Object-Oriented Languages 210
Sharing Data Between Two Companies 211
Validating the Document with the Document Type Definition (DTD) 212
Integrating the DTD into the XML Document 213
Using Cascading Style Sheets 220
Conclusion 223
References 223
12 Persistent Objects: Serialization and Relational Databases 225
Persistent Objects Basics 225
Saving the Object to a Flat File 227
Serializing a File 227
Implementation and Interface Revisited 229
What About the Methods? 231
Using XML in the Serialization Process 231
Writing to a Relational Database 234
Accessing a Relational Database 236
Loading the Driver 238
Making the Connection 238
The SQL Statements 239
Conclusion 242
References 242
Example Code Used in This Chapter 242
13 Objects and the Internet 247
Evolution of Distributed Computing 247
Object-Based Scripting Languages 248
A JavaScript Validation Example 250
Objects in a Web Page 253
JavaScript Objects 254
Web Page Controls 255
Sound Players 257
Movie Players 257
Flash 258
Distributed Objects and the Enterprise 258
The Common Object Request Broker Architecture (CORBA) 259
Web Services Definition 263
Web Services Code 267
Invoice.cs 267
Invoice.vb 268
Conclusion 270
References 270
14 Objects and Client/Server Applications 271
Client/Server Approaches 271
Proprietary Approach 272
Serialized Object Code 272
Client Code 273
Server Code 275
Running the Proprietary Client/Server Example 276
Nonproprietary Approach 278
Object Definition Code 278
Client Code 280
Server Code 281
Running the Nonproprietary Client/Server Example 283
Conclusion 283
References 284
Example Code Used in This Chapter 284
15 Design Patterns 287
Why Design Patterns? 288
Smalltalk's Model/View/Controller 289
Types of Design Patterns 290
Creational Patterns 291
Structural Patterns 295
Behavioral Patterns 298
Antipatterns 299
Conclusion 300
References 300
Example Code Used in This Chapter 301
Index 309
Preface
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Introduction
This Book's Scope
As the title indicates, this book is about the object-oriented (OO) thought process. Obviously, choosing the theme and title of the book are important decisions; however, these decisions were not all that simple. Numerous books deal with various levels of object orientation. Several popular books deal with topics including OO analysis, OO design, OO programming, design patterns, OO data (XML), the Unified Modeling Language (UML), OO Internet development, various OO programming languages, and many other topics related to OO development.
However, while pouring over all of these books, many people forget that all of these topics are built on a single foundation: how you think in OO ways. It is unfortunate, but software professionals often dive into these books without taking the appropriate time and effort to really understand the concepts behind the content.
I contend that learning OO concepts is not accomplished by learning a specific development method or a set of tools. Doing things in an OO manner is, simply put, a way of thinking. This book is all about the OO thought process.
Separating the methods and tools from the OO thought process is not easy. Many people are introduced to OO concepts via one of these methods or tools. For example, years ago, most C programmers were first introduced to object orientation by migrating directly to C++-before they were even remotely exposed to OO concepts. Other software professionals were first introduced to object orientation by presentations that included object models using UML-again, before they were even exposed directly to OO concepts. It is not unusual to find that programming books and courses defer OO concepts until later in the learning process.
It is important to understand the significant difference between learning OO concepts and using the methods and tools that support the paradigm. This came into focus for me before I worked on the first edition of this book when I read articles such as Craig Larman's 'What the UML Is-and Isn't,' In this article he states,
Unfortunately, in the context of software engineering and the UML diagramming language, acquiring the skills to read and write UML notation seems to sometimes be equated with skill in object-oriented analysis and design. Of course, this is not so, and the latter is much more important than the former. Therefore, I recommend seeking education and educational materials in which intellectual skill in object-oriented analysis and design is paramount rather than UML notation or the use of a case tool.
Although learning a modeling language is an important step, it is much more important to learn OO skills first. Learning UML before OO concepts is similar to learning how to read an electrical diagram without first knowing anything about electricity.
The same problem occurs with programming languages. As stated earlier, many C programmers moved into the realm of object orientation by migrating to C++ before being directly exposed to OO concepts. This would always come out in an interview. Many times developers who claim to be C++ programmers are simply C programmers using C++ compilers. Even now, with languages such as C# .NET, VB .NET, and Java well established, a few key questions in a job interview can quickly uncover a lack of OO understanding.
Early versions of Visual Basic are not OO. C is not OO, and C++ was developed to be backward compatible with C. Because of this, it is quite possible to use a C++ compiler (writing only C syntax) while forsaking all of C++'s OO features. Even worse, a programmer can use just enough OO features to make a program incomprehensible to OO and non-OO programmers alike.
Thus, it is of vital importance that while you're on the road to OO development, you first learn the fundamental OO concepts. Resist the temptation to jump directly into a programming language (such as VB .NET, C++, C# .NET or Java) or a modeling language (such as UML), and take the time to learn the object-oriented thought process.
In my first class in Smalltalk in the late 1980s, the instructor told the class that the new OO paradigm was a totally new way of thinking (despite the fact that it has been around since the 60s). He went on to say that although all of us were most likely very good programmers, about 10%-20% of us would never really grasp the OO way of doing things. If this statement is indeed true, it is most likely because some people never really take the time to make the paradigm shift and learn the underlying OO concepts.
What's New in the Third Edition
As stated often in this introduction, my vision for the first edition was primarily a conceptual book. Although I still adhere to this goal for the second and third editions, I have included several application topics that fit well with object-oriented concepts. For the third edition I expand on many of the topics of the second edition and well as include totally new chapters. These revised and updated concepts
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XML is used for object communication.
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Object persistence and serialization.
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XML integrated into the languages object definition.
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Adding properties to attributes.
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XML-based Internet applications.
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Client/Server technologies.
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Expanded code examples in Java, C# .NET and VB .NET.
The chapters that cover these topics are still conceptual in nature; however, many of the chapters include Java code that shows how these concepts are implemented. In this third edition, a code appendix is included that presents the chapter's examples in C# .NET and Visual Basic .NET.
The Intended Audience
This book is a general introduction to fundamental OO concepts with code examples to reinforce the concepts. One of the most difficult juggling acts was to keep the material conceptual while still providing a solid, technical code base. The goal of this book is to allow a reader to understand the concepts and technology without having a compiler at hand. However, if you do have a compiler available, then there is code to be investigated.
The intended audience includes business managers, designers, developers, programmers, project managers, and anyone who wants to gain a general understanding of what object orientation is all about. Reading this book should provide a strong foundation for moving to other books covering more advanced OO topics.
Of these more advanced books, one of my favorites remains Object-Oriented Design in Java by Stephen Gilbert and Bill McCarty. I really like the approach of the book, and have used it as a textbook in classes I have taught on OO concepts. I cite Object-Oriented Design in Java often throughout this book, and I recommend that you graduate to it after you complete this one.
Other books that I have found very helpful include Effective C++ by Scott Meyers, Classical and Object-Oriented Software Engineering by Stephen R. Schach, Thinking in C++ by Bruce Eckel, UML Distilled by Martin Flower, and Java Design by Peter Coad and Mark Mayfield.
The conceptual nature of this book provides a unique perspective in regards to other computer technology books. While books that focus on specific technologies, such as programming languages, struggle with the pace of change, this book has the luxury of presenting established concepts that, while certainly being fine-tuned, do not experience radical changes. With this in mind, many of the books that were referenced several years ago, are still referenced because the concepts are still fundamentally the same.
This Book's Scope
It should be obvious by now that I am a firm believer in becoming comfortable with the object-oriented thought process before jumping into a programming language or modeling language. This book is filled with examples of code and UML diagrams; however, you do not need to know a specific programming language or UML to read it. After all I have said about learning the concepts first, why is there so much Java, C# .NET, and VB .NET code and so many UML diagrams? First, they are all great for illustrating OO concepts. Second, both are vital to the OO process and should be addressed at an introductory level. The key is not to focus on Java, C# .NET, and VB .NET or UML, but to use them as aids in the understanding of the underlying concepts.
The Java, C# .NET and VB .NET examples in the book illustrate concepts such as loops and functions. However, understanding the code itself is not a prerequisite for understanding the concepts; it might be helpful to have a book at hand that covers specific languages syntax if you want to get more detailed.
I cannot state too strongly that this book does not teach Java, C# .NET, and VB .NET or UML, all of which can command volumes unto themselves. It is my hope that this book will whet your appetite for other OO topics, such as OO analysis, object-oriented design, and OO programming.
This Book's Conventions
The following conventions are used in this book:
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Code lines, commands, statements, and any other code-related terms appear in a monospace typeface.
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Placeholders that stand for what you should actually type appear in italic monospace. Text that you should type appears in bold monospace.
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Throughout the book, there are special sidebar elements, such as
Note - A Note presents interesting information related to the discussion-a little more insight or a pointer to some new technique.
Tip - A Tip offers advice or shows you an easier way of doing something.
Caution - A Caution alerts you to a possible problem and gives you advice on how to avoid it.
Source Code Used in This Book
You can download all the source code and examples discussed within this book from the publisher's website.
© Copyright Pearson Education. All rights reserved.
About the Authors
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Matt Weisfeld is an associate professor in business & technology at Cuyahoga Community College (Tri-C) in Cleveland, Ohio.A member of the information technology faculty, he focuses on programming, web development, and entrepreneurship. Prior to joining Tri-C,Weisfeld spent 20 years in the information technology industry gaining experience in software development, project management, small business management, corporate training, and part-time teaching. He holds an MS in computer science and an MBA in project management. Besides the first two editions of The Object-Oriented Thought Process, he has published two other computer books and articles in magazines and journals such as developer.com, Dr. Dobb's Journal, The C/C++ Users Journal, Software Development Magazine, Java Report, and the international journal Project Management.
