Table of Contents
Preface.
Acknowledgments.
I. WHAT ARE DESIGN PATTERNS?
1. Introduction. Defining Design Patterns.
The Learning Process.
Studying Design Patterns.
Notes on Object-Oriented Approaches.
The Java Foundation Classes.
Java Design Patterns.
2. UML Diagrams. Inheritance.
Interfaces.
Composition.
Annotation.
JVISION UML Diagrams.
Visual SlickEdit Project Files.
II. CREATIONAL PATTERNS.
3. The Factory Pattern. How a Factory Works.
Sample Code.
The Two Subclasses.
Building the SimpleFactory.
Factory Patterns in Math Computation.
Thought Questions.
4. The Factory Method. The Swimmer Class.
The Event Classes.
Straight Seeding.
Our Seeding Program.
Other Factories.
When to Use a Factory Method.
Thought Question.
5. The Abstract Factory Pattern. A GardenMaker Factory.
How the User Interface Works.
Adding More Classes.
Consequences of the Abstract Factory Pattern.
Thought Question.
6. The Singleton Pattern. Creating a Singleton Using a Static Method.
Exceptions and Instances.
Throwing an Exception.
Creating an Instance of the Class.
Providing a Global Point of Access to a Singleton Pattern.
The javax.comm Package as a Singleton.
Other Consequences of the Singleton Pattern.
Thought Question.
7. The Builder Pattern. An Investment Tracker.
Calling the Builders.
The List Box Builder.
The Check Box Builder.
Consequences of the Builder Pattern.
Thought Questions.
8. The Prototype Pattern. Cloning in Java.
Using the Prototype.
Using the Prototype Pattern.
Prototype Managers.
Cloning Using Serialization.
Consequences of the Prototype Pattern.
Thought Question.
Summary of Creational Patterns.
III. STRUCTURAL PATTERNS.
9. The Adapter Pattern. Moving Data between Lists.
Using the JFC JList Class.
Two-Way Adapters.
Pluggable Adapters.
Adapters in Java.
Thought Question.
10. The Bridge Pattern. The Class Diagram.
Extending the Bridge.
Java Beans as Bridges.
Consequences of the Bridge Pattern.
Thought Question.
11. The Composite Pattern. An Implementation of a Composite.
Computing Salaries.
The Employee Classes.
The Boss Class.
Building the Employee Tree.
Self-Promotion.
Doubly Linked List.
Consequences of the Composite Pattern.
A Simple Composite.
Composites in Java.
Other Implementation Issues.
Thought Questions.
12. The Decorator Pattern. Decorating a CoolButton.
Using a Decorator.
The Class Diagram.
Decorating Borders in Java.
Nonvisual Decorators.
Decorators, Adapters, and Composites.
Consequences of the Decorator Pattern.
Thought Questions.
13. The Faade Pattern. Building the Faade Classes.
Consequences of the Faade Pattern.
Notes on Installing and Running the dbFrame Program.
Thought Question.
14. The Flyweight Pattern. Discussion.
Example Code.
Flyweight Uses in Java.
Sharable Objects.
Copy-on-Write Objects.
Thought Question.
15. The Proxy Pattern. Sample Code.
Copy-on-Write.
Enterprise Java Beans.
Comparison with Related Patterns.
Thought Question.
Summary of Structural Patterns.
IV. BEHAVIORAL PATTERNS.
16. Chain of Responsibility Pattern. Applicability.
Sample Code.
The List Boxes.
Programming a Help System.
A Chain or a Tree?
Kinds of Requests.
Examples in Java.
Consequences of the Chain of Responsibility.
Thought Questions.
17. The Command Pattern. Motivation.
Command Objects.
Building Command Objects.
The Command Pattern.
The Command Pattern in the Java Language.
Consequences of the Command Pattern.
Providing Undo.
Thought Questions.
18. The Interpreter Pattern. Motivation.
Applicability.
Simple Report Example.
Interpreting the Language.
Objects Used in Parsing.
Reducing the Parsed Stack.
Implementing the Interpreter Pattern.
Consequences of the Interpreter Pattern.
Thought Question.
19. The Iterator Pattern. Motivation.
Enumerations in Java.
Sample Code.
Filtered Iterators.
Consequence of the Iterator Pattern.
Composites and Iterators.
Iterators in Java 1.2.
Thought Question.
20. The Mediator Pattern. An Example System.
Interactions between Controls.
Sample Code.
Mediators and Command Objects.
Consequences of the Mediator Pattern.
Single Interface Mediators.
Implementation Issues.
21. The Memento Pattern. Motivation.
Implementation.
Sample Code.
Consequences of the Memento Pattern.
Thought Question.
22. The Observer Pattern. Watching Colors Change.
The Message to the Media.
The JList as an Observer.
The MVC Architecture as an Observer.
The Observer Interface and Observable Class.
Consequences of the Observer Pattern.
Thought Questions.
23. The State Pattern. Sample Code.
Switching between States.
How the Mediator Interacts with the StateManager.
State Transitions.
Mediators and the God Class.
Consequences of the State Pattern.
Thought Questions.
24. The Strategy Pattern. Motivation.
Sample Code.
The Context Class.
The Program Commands.
The Line and Bar Graph Strategies.
Drawing Plots in Java.
Consequences of the Strategy Pattern.
Thought Question.
25. The Template Pattern. Motivation.
Kinds of Methods in a Template Class.
Template Method Patterns in Java.
Sample Code.
Templates and Callbacks.
Consequences of the Template Pattern.
Thought Question.
26. The Visitor Pattern. Motivation.
When to Use the Visitor Pattern.
Sample Code.
Visiting the Classes.
Visiting Several Classes.
Bosses are Employees, Too.
Catch-All Operations Using Visitors.
Double Dispatching.
Traversing a Series of Classes.
Consequence of the Visitor Pattern.
Thought Question.
V. DESIGN PATTERNS AND THE JAVA FOUNDATION CLASSES.
27. The JFC, or Swing. Installing and Using Swing.
Ideas behind Swing.
The Swing Class Hierarchy.
28. Writing a Simple JFC Program. Setting the Look and Feel.
Setting the Window Close Box.
Making a JxFrame Class.
A Simple Two-Button Program.
More on JButton.
29. Radio Buttons and Toolbars. Radio Buttons.
The JToolBar.
JToggleButton.
A Sample Button Program.
30. Menus and Actions. Action Objects.
Design Patterns in the Action Object.
31. The JList Class. List Selections and Events.
Changing a List Display Dynamically.
A Sorted JList with a ListModel.
Sorting More-Complicated Objects.
Getting Database Keys.
Adding Pictures in List Boxes.
Programs on the CD-ROM.
32. The JTable Class. A Simple JTable Program.
Cell Renderers.
Rendering Other Kinds of Classes.
Selecting Cells in a Table.
Patterns Used in This Image Table.
33. The JTree Class. The TreeModel Interface.
Summary.
IV. CASE STUDIES.
34. Sandy and the Mediator. 35. Herb's Text Processing Tangle. 36. Mary's Dilemma. Bibliography.
Preface
This is a practical book that tells you how to write Java programs using some of the most common design patterns. It is structured as a series of short chapters, each describing a design pattern and giving one or more complete, working, visual example programs that use that pattern. Each chapter also includes Unified Modeling Language (UML) diagrams illustrating how the classes interact.
This book is not a "companion" book to the well-known Design Patterns text Gamma, 1995 by the "Gang of Four." Rather, it is a tutorial for people who want to learn what design patterns are about and how to use them in their work. You need not have read Design Patterns to gain from reading this book, but when you are done here you might want to read or reread that book to gain additional insights.
In this book, you will learn that design patterns are a common way to organize objects in your programs to make those programs easier to write and modify. You'll also see that by familiarizing yourself with these design patterns, you will gain a valuable vocabulary for discussing how your programs are constructed.
People come to appreciate design patterns in different ways--from the highly theoretical to the intensely practical--and when they finally see the great power of these patterns, they experience an "Aha!" moment. Usually this moment means that you suddenly had an internal picture of how that pattern can help you in your work.
In this book, we try to help you form that conceptual idea, or gestalt, by describing the pattern in as many ways as possible. The book is organized into six main sections:
- An introductory description
- A description of patterns grouped into three sections: Creational, Structural, and Behavioral
- A description of the Java Foundation Classes (JFC) showing the patterns they illustrate
- A set of case studies where patterns have been helpful
For each pattern, we start with a brief verbal description and then build simple example programs. Each example is a visual program that you can run and examine so as to make the pattern as concrete as possible. All of the example programs and their variations are on the CD-ROM that accompanies this book. In that way, you can run them, change them, and see how the variations that you create work.
All of the programs are based on Java 1.2, and most use the JFC. If you haven't taken the time to learn how to use these classes, there is a tutorial covering the basics in Appendix A where we also discuss some of the patterns that they illustrate.
Since each of the examples consists of a number of Java files for each of the classes we use in that example, we also provide a Visual SlickEdit project file for each example and place each example in a separate subdirectory to prevent any confusion.
As you leaf through the book, you'll see screen shots of the programs we developed to illustrate the design patterns; these provide yet another way to reinforce your learning of these patterns. You'll also see UML diagrams of these programs that illustrate the interactions between classes in yet another way. UML diagrams are just simple box and arrow illustrations of classes and their inheritance structure, with the arrows pointing to parent classes and dotted arrows pointing to interfaces. If you are unfamiliar with UML, we provide a simple introduction in the first chapter.
Finally, since we used JVISION to create the UML diagrams in each chapter, we provide the original JVISION diagram files for each pattern as well, so you can use your own copy of JVISION to play with them.
When you finish this book, you'll be comfortable with the basics of design patterns and will be able to start using them in your day to day Java programming work.
James W. Cooper
Wilton, CT
Nantucket, MA
November, 1999
0201485397P04062001