Agile Java¿: Crafting Code with Test-Driven Development

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Learn what it takes to build a professional, robust software system using Java, integrating the best features of Test-Driven Development.

° Gives you the skills to translate requirements into tests, and tests into working code

° Seamlessly integrates the new language features of Java 5 into the learning experience

° Based on the author's experience instructing classes using TDD as the driving force-- and TDD is a great source of immediate feedback

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Crafting Java Code with Test-Driven Development: the Basics

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Table of Contents

About the Author.

Foreword.

Acknowledgments.

Introduction.

    Who Is This Book For?

    What This Book Is Not

    How to Use This Book

    Exercises

    Conventions Used in This Book

An Agile Overview.

    What Is “Agile?”

    What Is Java?

    Why OO?

    What Is an Object?

    What Are Classes?

    Why UML?

    What Is Inheritance?

    Why Test-Driven Development?

Setting Up.

    Software You’ll Need

    Does It Work?

    Compiling Hello World

    Executing Hello World

    Still Stuck?

Lesson 1: Getting Started.

    Testing

    Design

    A Simple Test

    JUnit

    Adding a Test

    Creating a Student

    Creating the Student Class

    Constructors

    Local Variables

    Returning a Value from a Method

    Assertions

    Instance Variables

    Summarizing the Test

    Refactoring

    this

    private

    Naming Conventions

    Whitespace

    Exercises

Lesson 2: Java Basics.

    CourseSession

    Enrolling Students

    int

    Initialization

    Default Constructors

    Suites

    The SDK and java.util.ArrayList

    Adding Objects

    Incremental Refactoring

    Objects in Memory

    Packages and the import Statement

    The java.lang Package

    The Default Package and the package Statement

    The setup Method

    More Refactoring

    Class Constants

    Dates

    Overload Constructors

    Deprecation Warnings

    Refactoring

    Creating Dates with Calendar

    Comments

    Javadoc Comments

    Exercises

Lesson 3: Strings and Packages.

    Characters and Strings

    Strings

    StringBuilder

    System Properties

    Looping Through All Students

    Single-Responsibility Principle

    Refactoring

    System.out

    Using System.out

    Refactoring

    Package Structure

    Access Modifiers

    Using Ant

    Exercises

Lesson 4: Class Methods and Fields.

    Class Methods

    Class Variables

    Operating on Class Variables with Class Methods

    Static Import

    Incrementing

    Factory Methods

    Simple Design

    Static Dangers

    Using Statics: Various Notes

    Jeff’s Rule of Statics

    Booleans

    Tests as Documentation

    More on Initialization

    Exceptions

    Revisiting Primitive-Type Field Initialization

    Exercises

Lesson 5: Interfaces and Polymorphism.

    Sorting: Preparation

    Sorting: Collections.sort

    CourseReportTest

    Interfaces

    Why Interfaces

    Implementing Comparable

    Sorting on Department and Number

    The if Statement

    Grading Students

    Floating-Point Numbers

    Testing Grades

    Refactoring

    Enums

    Polymorphism

    Using Interface References

    ArrayList and the List Interface

    Exercises

Lesson 6: Inheritance.

    The switch Statement

    Case Labels Are Just Labels

    Maps

    Inheritance

    Abstract Classes

    Extending Methods

    Refactoring

    Enhancing the Grade Enum

    Summer Course Sessions

    Calling Superclass Constructors

    Refactoring

    More on Constructors

    Inheritance and Polymorphism

    The Principle of Subcontracting

    Exercises

Lesson 7: Legacy Elements.

    Looping Constructs

    Breaking Up a Student’s Name

    The while Loop

    Comparing Java Loops

    Refactoring

    Looping Control Statements

    The Ternary Operator

    Legacy Collections

    Iterators

    Iterators and the for-each Loop

    Casting

    Wrapper Classes

    Arrays

    Refactoring

    Exercises

Lesson 8: Exceptions and Logging.

    Exceptions

    Dealing With Exceptions

    Checked Exceptions

    Exception Hierarchy

    Creating Your Own Exception Type

    Checked Exceptions vs. Unchecked Exceptions

    Messages

    Catching Multiple Exceptions

    Rethrowing Exceptions

    Stack Traces

    The finally Block

    Refactoring

    Logging

    Logging in Java

    Testing Logging

    Logging to Files

    Testing Philosophy for Logging

    More on FileHandler

    Logging Levels

    Logging Hierarchies

    Additional Notes on Logging

    Exercises

Lesson 9: Maps and Equality.

    Logical Operators

    Short-Circuiting

    Hash Tables

    Courses

    Refactoring Session

    Equality

    The Contract for Equality

    Apples and Oranges

    Collections and Equality

    Hash Tables

    Collisions

    An Ideal Hash Algorithm

    A Final Note on hashCode

    More on Using HashMaps

    Additional Hash Tables and Set Implementations

    toString

    Strings and Equality

    Exercises

Lesson 10: Mathematics.

    BigDecimal

    More on Primitive Numerics

    Integer Math

    Numeric Casting

    Expression Evaluation Order

    NaN

    Infinity

    Numeric Overflow

    Bit Manipulation

    Java.lang.Math

    Numeric Wrapper Classes

    Random Numbers

    Exercises

Lesson 11: IO.

    Organization

    Character Streams

    Writing to a File

    Java.io.File

    Byte Streams and Conversion

    A Student User Interface

    Testing the Application

    Data Streams

    CourseCatalog

    Advanced Streams

    Object Streams

    Random Access Files

    The Student Directory

    sis.db.DataFileTest

    Static Nested Classes and Inner Classes

    sis.db.DataFile

    sis.db.KeyFileTest

    sis.db.KeyFile

    sis.util.IOUtilTest

    sis.util.IOUtil

    sis.util.TestUtil

    Developing the Solution

    Exercises

Lesson 12: Reflection and Other Advanced Topics.

    Mock Objects Revisited

    The Jim Bob ACH Interface

    The Mock Class

    The Account Class Implementation

    Anonymous Inner Classes

    Adapters

    Accessing Variables from the Enclosing Class

    Tradeoffs

    Reflection

    Using JUnit Code

    The Class Class

    Building the Suite

    Class Modifiers

    Dynamic Proxy

    A Secure Account Class

    Building the Secure Account Solution

    The SecureProxy Class

    Problems With Reflection

    Exercises

Lesson 13: Mulithreading.

    Multithreading

    Search Server

    The Search Class

    Less Dependent Testing

    The Server

    Waiting in the Test

    Creating and Running Threads

    Cooperative and Preemptive Multitasking

    Synchronization

    Creating Threads with Runnable

    Synchronized

    Synchronized Collections

    BlockingQueue

    Stopping Threads

    Wait/Notify

    Additional Notes on wait and notify

    Locks and Conditions

    Thread Priorities

    Deadlocks

    ThreadLocal

    The Timer Class

    Thread Miscellany

    Summary: Basic Design Principles for Synchronization

    Exercises

Lesson 14: Generics.

    Parameterized Types

    Collection Framework

    Multiple Type Parameters

    Creating Parameterized Types

    Erasure

    Upper Bounds

    Wildcards

    Implications of Using Wildcards

    Generic Methods

    Wildcard Capture

    Super

    Additional Bounds

    Raw Types

    Checked Collections

    Arrays

    Additional Limitations

    Reflection

    Final Notes

    Exercises

Lesson 15: Assertions and Annotations.

    Assertions

    The assert Statement vs. JUnit Assert Methods

    Annotations

    Building a Testing Tool

    TestRunnerTest

    TestRunner

    The @TestMethod Annotation

    Retention

    Annotation Targets

    Skipping Test Methods

    Modifying TestRunner

    Single-Value Annotations

    A TestRunner User Interface Class

    Array Parameters

    Multiple Parameter Annotations

    Default Values

    Additional Return Types and Complex Annotation Types

    Package Annotations

    Compatibility Considerations

    Additional Notes on Annotations

    Summary

    Exercises

Additional Lesson I: Swing, Part 1.

    Swing

    Getting Started

    Swing Application Design

    Panels

    Refactoring

    More Widgets

    Refactoring

    Button Clicks and ActionListeners

    List Models

    The Application

    Layout

    GridBagLayout

    Moving Forward

Additional Lesson II: Swing, Part 2.

    Miscellaneous Aesthetics

    Feel

    Tables

    Feedback

    Responsiveness

    Remaining Tasks

    Final Notes

Additional Lesson III: Java Miscellany.

    JARs

    Regular Expressions

    Cloning and Covariance

    JDBC

    Internationalization

    Call by Reference versus Call by Value

    Java Periphery

    What Else Is There?

Appendix A: An Agile Java Glossary.

Appendix B: Java Operator Precedence Rules.

Appendix C: Getting Started with IDEA.

    IDEA

    The Hello Project

    Running Tests

    Taking Advantage of IDEA

Agile Java References.

Index.

Preface

Introduction

I am a software craftsman 1 . I have spent much of my software development career trying to be able to quickly build solutions to problems. At the same time I have tried to ensure that my solutions demonstrate carefully crafted code. I strive for perfection in code, yet I know that it is unattainable, particularly with the constant pressure from business to get product out the door. I take modest pride in the code that I build daily, yet I look on the very code that I wrote the day before and wonder, "what the heck was I thinking?" This is what keeps the craft challenging to me—the constant desire to figure out how to do things a little better the next time, and with a little less pain than this time.

Agile Java represents a successful approach to learning and mastering Java development. It is based on the way I have learned to best teach programming, and to learn new programming languages myself: using test-driven development (TDD). TDD is a technique that introduces a large amount of low-level feedback. This feedback allows you to more quickly see the results of your actions. Using TDD, you will learn how to craft Java code to produce solid object-oriented designs and highly maintainable, high quality systems.

I have used TDD in production systems for over three years, and am still amazed at what it does for me. It has improved the quality of my code; it has taught me new things each week; it has made me more productive. I have also created and taught language courses using TDD, both at my own company and at Object Mentor (who continues to teach their language courses with this approach).

Prior to learning TDD, I spent more than fifteen years learning, developing in, and teaching languages the "classic" way—without using tests to drive the development. The student builds and executes example code. The student obtains feedback on what the code is teaching by viewing the output from code execution. While this is a perfectly valid approach, my anecdotal experience is that using it results in less-than-ideal retention of language details.

In contrast, the high volume of rapid feedback in TDD constantly reinforces correct coding and quickly points out incorrect coding. The classic code-run-and-observe approach provides feedback, but at a much slower rate. Unfortunately, it is currently the predominant method of teaching programming.

Others have attempted more innovative approaches to teaching. In the 1990s, Adele Goldberg created a product known as LearningWorks designed for teaching younger students. It allowed a user to directly manipulate visual objects by dynamically executing bits of code. The user saw immediate results from their actions. A recent Java training tool uses a similar approach. It allows the student to execute bits of code to produce visual effects on "live" objects.

The problem with approaches like these is that they are bound to the learning environment. Once you complete the training, you must still learn how to construct your own system from the ground up, without the use of these constrained tools. By using TDD as the driver for learning, you are taught an unbounded technique that you can continue to use in your professional software development career.

Agile Java takes the most object-oriented approach feasible. Part of the difficulty in learning Java is the 'bootstrapping" involved. What is the minimum you must learn in order to be able to write classes of some substance?

Most books start by teaching you the prototypical first Java program—the "hello world" application. But it is quite a mouthful: class Hello { public static void main(String args) { System.out.println("hello world"); } } . This brief program contains at least a dozen concepts that you must ultimately learn. Worse, out of those dozen concepts, at least three are non-object-oriented concepts that you are better off learning much later.

In this book, you will learn the right way to code from the start, and come back to fully understand "hello world" later in the book 2 . Using TDD, you will be able to write good object-oriented code immediately. You'll still have a big initial hurdle to get over, but this approach keeps you from having to first understand not-very-object-oriented concepts such as static methods and arrays. You will learn all core Java concepts in due time, but your initial emphasis is on objects.

Agile Java presents a cleaner break from the old way of doing things. It allows you to pretend for a while that there was never a language called C, the syntactical basis for Java that has been around for 30 years. While C is a great language, its imprint on Java left a quite a few constructs that can distract you from building good object-oriented systems. Using Agile Java, you can learn the right way of doing things before having to understand these legacies of the Java language.

Who is this Book For

I designed Agile Java for new programmers who want to learn Java as their first language. The book can also be effective for programmers familiar with TDD, but new to Java, or vice versa. Experienced Java developers may find that going through Agile Java presents them with a new, hopefully better, way of approaching things.

This edition of Agile Java covers Java 2 Standard Edition (J2SE) version 5.0.

Sun has made available dozens of class libraries, or APIs (application programming interfaces), that enhance the core Java language. Some examples: JMS (Java Messaging Service) provides a definition for standard messaging-based solutions. EJBs (Enterprise Java Beans) provide a means of building component-based software for large enterprise solutions. JDBC (Java DataBase Connectivity) supplies a standard interface for interacting with relational databases. About a dozen of the advanced APIs are collectively known as J2EE (Java 2 Enterprise Edition). Many of the APIs require entire books for comprehensive coverage. There are dozens of books on J2EE.

This book covers only a few of the additional APIs at an introductory level. Technologies that are used pervasively in the majority of enterprise applications, such as logging, JDBC, and Swing, are presented in Agile Java. Some of the information (for example, logging) will teach you all you need to know for most applications. Other lessons (for example, Swing and JDBC) will teach you a basic understanding of the technology. These lessons will provide you with enough to get started, as well as where to go for more information.

If you are developing mobile applications, you will be using J2ME (Java 2 Micro Edition). J2ME is a version of Java geared toward environments with limited resources, such as cell phones. J2ME has some significant limitations in comparison to J2SE. This book does not discuss anything specific with respect to J2ME. However, most of the core techniques and concepts of Java development are applicable to the J2ME environment.

In order to use any of these add-on Java technologies, you must first understand the core language and libraries provided in J2SE. Agile Java will help you build that knowledge.

What This Book is Not

Agile Java is not an exhaustive treatise on every aspect of the Java language. It instead provides an agile approach to learning the language. Rather than give you all the fish, I teach you how to fish and sometimes where to find the fish. Agile Java will teach you the majority of the core language concepts. Indeed, upon completing the core fifteen lessons, you will be able to produce quality production Java code. However, there are bound to be a few esoteric language features and nuances that I do not cover in the book.

One way to become familiar with the dusty corners of the language is to peruse the Java Language Specification (JLS). The second edition of the language specification is available at http://java.sun.com/docs/books/jls. This edition covers versions of Java up to but not including J2SE 5.0. A third edition of the JLS is in the works at the time I write this. You can find a maintenance review version at: http://java.sun.com/docs/books/jls/java_language-3_0-mr-spec.zip

For additional understanding of what is in the Java API library, the Java API documentation and actual source code is the best place to go.

Agile Java is not a certification study guide. It will not prepare you for a certification exam. A good book on certification will teach you how to take a test. It will also teach you how to decipher (deliberately) poorly written code that shouldn't have been written that way in the first place. Agile Java will teach you instead how to write professional Java code.

Agile Java doesn't attempt to coddle you or distract you with flashing headlines and cute images. Learning to program is a significant challenge. Programming involves thinking and solving problems—it is not an easy undertaking for idiots or dummies. I've attempted to avoid insulting your intelligence in this book. That being said, I have tried to make Agile Java an enjoyable, easy read. It is a conversation between you and me, much like the conversations you will continue to have in your professional development career. It's also a conversation between you and your computer.

TDD Disclaimer

Some developers experienced in TDD will note stylistic differences between their approach and my approach(es) in Agile Java. There are many ways to do TDD. None of these techniques are perfect or ordained as the absolute right way to do things. Do whatever works best for you. Do what makes the most sense, as long as it doesn't violate the basic tenets set forth in Agile Java.

Readers will also find areas in which the code could be improved 3 . Even as a beginning developer, you no doubt will encounter code in Agile Java that you don't like. Let me know. Send in your suggestions, and I may incorporate them in the next edition. And fix your own implementations. You can improve almost any code or technique . Do!

After the first lesson in Agile Java, the tests appear wholesale, as if they were coded in one fell swoop. This is not the case: each test was built assertion by assertion, in much smaller increments than the book can afford to present. Keep this in mind when writing your own code—one of the most important aspects of TDD is taking small, small steps with constant feedback. And when I say small, I mean small! If you think you're taking small steps, try taking even smaller steps.

How to Use This Book

The core of Agile Java is fifteen lessons of about 30 pages each. You will start with baby steps in Java, TDD, and OO. You will finish with a strong foundation for professional Java development.

The core lessons are sequential. You should start at lesson 1 and complete each lesson before proceeding to the next. Once you have completed section 1, you should have a solid understanding of how to build robust Java code.

If you haven't completed the core lessons, you should not assume you know how to write good Java code! (Even if you have completed the lessons, you're not an expert... yet.) Each lesson builds upon the previous. If you stop short of completing the lessons, your lack of full understanding may lead you to construct poor code.

Each lesson starts with a brief overview of the topics to be discussed. The remainder of the lesson is a narrative. I describe each language feature in the text, specified by test code. I demonstrate each feature in a corresponding code implementation. I have interspersed discussions of TDD technique, OO principles, and good development practices in these lessons.

I've supplied three additional lessons to cover a few more Java topics. Two of the lessons present an introduction to Java's tool for user interface development, Swing. These two lessons will provide you with enough information to begin building robust user interface applications in Java. But the bigger intent is to give you some ideas for how to build them using TDD. The third additional lesson presents an overview for a number of Java topics, things that most Java developers will want to know.

For the most effective learning experience, you should follow along with the lessons by entering and executing each bit of test and implementation code as I present it. While the code is available for downloading (see the next paragraph), I highly recommend that you type each bit of code yourself. Part of doing TDD correctly is getting a good understanding of the rhythm involved in going back and forth between the tests and the code. If you just download the code and execute it, you're not going to learn nearly as much. The tactile response of the keyboard seems to impart a lot of learning.

However, who am I to make you work in a certain way? You may choose to download the code from http://www.LangrSoft.com/agileJava/code . I've organized this code by lesson. I have made available the code that is the result of working each lesson— in the state it exists by the end of the lesson . This will make it easier for you to pick up at any point, particularly since many of the examples carry through to subsequent lessons.

Exercises

Each of the fifteen core lessons in Agile Java has you build bits and pieces of a student information system for a university. I chose this single common theme to help demonstrate how you can incrementally build upon and extend existing code. Each lesson also finishes with a series of exercises. Instead of the student information system, the bulk of the exercises, provided by Jeff Bay, have you build bits and pieces of a chess application.

Some of the exercises are involved and quite challenging. But I highly recommend that you do every one. The exercises are where the real learning starts—you're figuring out how to solve problems using Java, without my help. Doing all of the exercises will give you a second opportunity to let each lesson sink in.

1 See McBreen2000

2 Don't fret, though: you'll actually start with the "hello world" application, in order to ensure you can compile and execute Java code. But you won't have to understand it all until later.

3 A constant developer pair would have helped.

© Copyright Pearson Education. All rights reserved.

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