Introduction

Like any human language, Java provides a way to express concepts. If successful, this medium of expression will be significantly easier and more flexible than the alternatives as problems grow larger and more complex.

You can’t look at Java as just a collection of features—some of the features make no sense in isolation. You can use the sum of the parts only if you are thinking about design, not simply coding. And to understand Java in this way, you must understand the problems with it and with programming in general. This book discusses programming problems, why they are problems, and the approach Java has taken to solve them. Thus, the set of features I explain in each chapter are based on the way I see a particular type of problem being solved with the language. In this way I hope to move you, a little at a time, to the point where the Java mindset becomes your native tongue.

Throughout, I’ll be taking the attitude that you want to build a model in your head that allows you to develop a deep understanding of the language; if you encounter a puzzle you’ll be able to feed it to your model and deduce the answer.

This book assumes that you have some programming familiarity: you understand that a program is a collection of statements, the idea of a subroutine/function/macro, control statements such as “if” and looping constructs such as “while,” etc. However, you might have learned this in many places, such as programming with a macro language or working with a tool like Perl. As long as you’ve programmed to the point where you feel comfortable with the basic ideas of programming, you’ll be able to work through this book. Of course, the book will be easier for the C programmers and more so for the C++ programmers, but don’t count yourself out if you’re not experienced with those languages (but come willing to work hard; also, the multimedia CD that accompanies this book will bring you up to speed on the basic C syntax necessary to learn Java). I’ll be introducing the concepts of object-oriented programming (OOP) and Java’s basic control mechanisms, so you’ll be exposed to those, and the first exercises will involve the basic control-flow statements.

Although references will often be made to C and C++ language features, these are not intended to be insider comments, but instead to help all programmers put Java in perspective with those languages, from which, after all, Java is descended. I will attempt to make these references simple and to explain anything that I think a non- C/C++ programmer would not be familiar with.

At about the same time that my first book Using C++ (Osborne/McGraw-Hill, 1989) came out, I began teaching that language. Teaching programming languages has become my profession; I’ve seen nodding heads, blank faces, and puzzled expressions in audiences all over the world since 1989. As I began giving in-house training with smaller groups of people, I discovered something during the exercises. Even those people who were smiling and nodding were confused about many issues. I found out, by chairing the C++ track at the Software Development Conference for a number of years (and later the Java track), that I and other speakers tended to give the typical audience too many topics too fast. So eventually, through both variety in the audience level and the way that I presented the material, I would end up losing some portion of the audience. Maybe it’s asking too much, but because I am one of those people resistant to traditional lecturing (and for most people, I believe, such resistance results from boredom), I wanted to try to keep everyone up to speed.

For a time, I was creating a number of different presentations in fairly short order. Thus, I ended up learning by experiment and iteration (a technique that also works well in Java program design). Eventually I developed a course using everything I had learned from my teaching experience—one that I would be happy giving for a long time. It tackles the learning problem in discrete, easy-to-digest steps, and in a hands-on seminar (the ideal learning situation) there are exercises following each of the short lessons. I now give this course in public Java seminars, which you can find out about at www.BruceEckel.com. (The introductory seminar is also available as a CD ROM. Information is available at the same Web site.)

The feedback that I get from each seminar helps me change and refocus the material until I think it works well as a teaching medium. But this book isn’t just seminar notes—I tried to pack as much information as I could within these pages, and structured it to draw you through onto the next subject. More than anything, the book is designed to serve the solitary reader who is struggling with a new programming language.

Like my previous book Thinking in C++, this book has come to be structured around the process of teaching the language. In particular, my motivation is to create something that provides me with a way to teach the language in my own seminars. When I think of a chapter in the book, I think in terms of what makes a good lesson during a seminar. My goal is to get bite-sized pieces that can be taught in a reasonable amount of time, followed by exercises that are feasible to accomplish in a classroom situation.

My goals in this book are to:

The Java language and libraries from Sun Microsystems (a free download) come with documentation in electronic form, readable using a Web browser, and virtually every third party implementation of Java has this or an equivalent documentation system. Almost all the books published on Java have duplicated this documentation. So you either already have it or you can download it, and unless necessary, this book will not repeat that documentation because it’s usually much faster if you find the class descriptions with your Web browser than if you look them up in a book. (Plus it will be up-to-date.) This book will provide extra descriptions of the classes only when it’s necessary to supplement the documentation so you can understand a particular example.

This book was designed with one thing in mind: the way people learn the Java language. Seminar audience feedback helped me understand the difficult parts that needed illumination. In the areas where I got ambitious and included too many features all at once, I came to know—through the process of presenting the material—that if you include a lot of new features, you need to explain them all, and this easily compounds the student’s confusion. As a result, I’ve taken a great deal of trouble to introduce the features as few at a time as possible.

The goal, then, is for each chapter to teach a single feature, or a small group of associated features, in such a way that no additional features are relied upon. That way you can digest each piece in the context of your current knowledge before moving on.

Here is a brief description of the chapters contained in the book, which correspond to lectures and exercise periods in my hands-on seminars.

Chapter 1: Introduction to Objects

This chapter is an overview of what object-oriented programming is all about, including the answer to the basic question “What’s an object?”, interface vs. implementation, abstraction and encapsulation, messages and functions, inheritance and composition, and the all-important polymorphism. You’ll also get an overview of issues of object creation such as constructors, where the objects live, where to put them once they’re created, and the magical garbage collector that cleans up the objects that are no longer needed. Other issues will be introduced, including error handling with exceptions, multithreading for responsive user interfaces, and networking and the Internet. You’ll learn what makes Java special, why it’s been so successful, and about object-oriented analysis and design.

Chapter 2: Everything is an Object

This chapter moves you to the point where you can write your first Java program, so it must give an overview of the essentials, including the concept of a reference to an object; how to create an object; an introduction to primitive types and arrays; scoping and the way objects are destroyed by the garbage collector; how everything in Java is a new data type (class) and how to create your own classes; functions, arguments, and return values; name visibility and using components from other libraries; the static keyword; and comments and embedded documentation.

Chapter 3: Controlling Program Flow

This chapter begins with all of the operators that come to Java from C and C++. In addition, you’ll discover common operator pitfalls, casting, promotion, and precedence. This is followed by the basic control-flow and selection operations that you get with virtually any programming language: choice with if-else; looping with for and while; quitting a loop with break and continue as well as Java’s labeled break and labeled continue (which account for the “missing goto” in Java); and selection using switch. Although much of this material has common threads with C and C++ code, there are some differences. In addition, all the examples will be full Java examples so you’ll get more comfortable with what Java looks like.

Chapter 4: Initialization & Cleanup

This chapter begins by introducing the constructor, which guarantees proper initialization. The definition of the constructor leads into the concept of function overloading (since you might want several constructors). This is followed by a discussion of the process of cleanup, which is not always as simple as it seems. Normally, you just drop an object when you’re done with it and the garbage collector eventually comes along and releases the memory. This portion explores the garbage collector and some of its idiosyncrasies. The chapter concludes with a closer look at how things are initialized: automatic member initialization, specifying member initialization, the order of initialization, static initialization and array initialization.

Chapter 5: Hiding the Implementation

This chapter covers the way that code is packaged together, and why some parts of a library are exposed while other parts are hidden. It begins by looking at the package and import keywords, which perform file-level packaging and allow you to build libraries of classes. The subject of directory paths and file names is also examined. The remainder of the chapter looks at the public, private, and protected keywords, the concept of “friendly” access, and what the different levels of access control mean when used in various contexts.

Chapter 6: Reusing Classes

The concept of inheritance is standard in virtually all OOP languages. It’s a way to take an existing class and add to its functionality (as well as change it, the subject of Chapter 7). Inheritance is often a way to reuse code by leaving the “base class” the same, and just patching things here and there to produce what you want. However, inheritance isn’t the only way to make new classes from existing ones. You can also embed an object inside your new class with composition. In this chapter you’ll learn about these two ways to reuse code in Java, and how to apply them.

Chapter 7: Polymorphism

On your own, you might take nine months to discover and understand polymorphism, a cornerstone of OOP. Through small, simple examples you’ll see how to create a family of types with inheritance and manipulate objects in that family through their common base class. Java’s polymorphism allows you to treat all objects in this family generically, which means the bulk of your code doesn’t rely on specific type information. This makes your programs extensible, so building programs and code maintenance is easier and cheaper.

Chapter 8: Interfaces & Inner Classes

Java provides a third way to set up a reuse relationship, through the interface, which is a pure abstraction of the interface of an object. The interface is more than just an abstract class taken to the extreme, since it allows you to perform a variation on C++’s “multiple inheritance,” by creating a class that can be upcast to more than one base type.

At first, inner classes look like a simple code hiding mechanism: you place classes inside other classes. You’ll learn, however, that the inner class does more than that—it knows about and can communicate with the surrounding class—and that the kind of code you can write with inner classes is more elegant and clear, although it is a new concept to most and takes some time to become comfortable with design using inner classes.

Chapter 9: Holding your Objects

It’s a fairly simple program that has only a fixed quantity of objects with known lifetimes. In general, your programs will always be creating new objects at a variety of times that will be known only while the program is running. In addition, you won’t know until run-time the quantity or even the exact type of the objects you need. To solve the general programming problem, you need to create any number of objects, anytime, anywhere. This chapter explores in depth the container library that Java 2 supplies to hold objects while you’re working with them: the simple arrays and more sophisticated containers (data structures) such as ArrayList and HashMap.

Chapter 10: Error Handling with Exceptions

The basic philosophy of Java is that badly-formed code will not be run. As much as possible, the compiler catches problems, but sometimes the problems—either programmer error or a natural error condition that occurs as part of the normal execution of the program—can be detected and dealt with only at run-time. Java has exception handling to deal with any problems that arise while the program is running. This chapter examines how the keywords try, catch, throw, throws, and finally work in Java; when you should throw exceptions and what to do when you catch them. In addition, you’ll see Java’s standard exceptions, how to create your own, what happens with exceptions in constructors, and how exception handlers are located.

Chapter 11: The Java IO System

Theoretically, you can divide any program into three parts: input, process, and output. This implies that IO (input/output) is an important part of the equation. In this chapter you’ll learn about the different classes that Java provides for reading and writing files, blocks of memory, and the console. The distinction between “old” IO and “new” Java IO will be shown. In addition, this section examines the process of taking an object, “streaming” it (so that it can be placed on disk or sent across a network) and reconstructing it, which is handled for you with Java’s object serialization. Also, Java’s compression libraries, which are used in the Java ARchive file format (JAR), are examined.

Chapter 12: Run-Time Type Identification

Java run-time type identification (RTTI) lets you find the exact type of an object when you have a reference to only the base type. Normally, you’ll want to intentionally ignore the exact type of an object and let Java’s dynamic binding mechanism (polymorphism) implement the correct behavior for that type. But occasionally it is very helpful to know the exact type of an object for which you have only a base reference. Often this information allows you to perform a special-case operation more efficiently. This chapter explains what RTTI is for, how to use it and how to get rid of it when it doesn’t belong there. In addition, the Java reflection mechanism is introduced.

Chapter 13: Creating Windows and Applets

Java comes with the “Swing” GUI library, which is a set of classes that handle windowing in a portable fashion. These windowed programs can either be applets or stand-alone applications. This chapter is an introduction to Swing and the creation of World Wide Web applets. The important “Java Beans” technology is introduced. This is fundamental for the creation of Rapid-Application Development (RAD) program-building tools.

Chapter 14: Multiple Threads

Java provides a built-in facility to support multiple concurrent subtasks, called threads, running within a single program. (Unless you have multiple processors on your machine, this is only the appearance of multiple subtasks.) Although these can be used anywhere, threads are most apparent when trying to create a responsive user interface so, for example, a user isn’t prevented from pressing a button or entering data while some processing is going on. This chapter looks at the syntax and semantics of multithreading in Java.

Chapter 15: Distributed Computing

All the Java features and libraries seem to really come together when you start writing programs to work across networks. This chapter explores communication across networks and the Internet, and the classes that Java provides to make this easier. It introduces the very important concepts of Servlets and JSPs (for server-side programming), along with Java DataBase Connectivity (JDBC), and Remote Method Invocation (RMI). Finally, there’s an introduction to the new technologies of JINI, JavaSpaces, and Enterprise JavaBeans (EJBs).

Appendix A: Passing & Returning Objects

Since the only way you talk to objects in Java is through references, the concepts of passing an object into a function and returning an object from a function have some interesting consequences. This appendix explains what you need to know to manage objects when you’re moving in and out of functions, and also shows the String class, which uses a different approach to the problem.

Appendix B: The Java Native Interface (JNI)

A totally portable Java program has serious drawbacks: speed and the inability to access platform-specific services. When you know the platform that you’re running on, it’s possible to dramatically speed up certain operations by making them native methods, which are functions that are written in another programming language (currently, only C/C++ is supported). This appendix gives you enough of an introduction to this feature that you should be able to create simple examples that interface with non-Java code.

Appendix C: Java Programming Guidelines

This appendix contains suggestions to help guide you while performing low-level program design and writing code.

Appendix D: Recommended Reading

A list of some of the Java books I’ve found particularly useful.

I’ve discovered that simple exercises are exceptionally useful to complete a student’s understanding during a seminar, so you’ll find a set at the end of each chapter.

Most exercises are designed to be easy enough that they can be finished in a reasonable amount of time in a classroom situation while the instructor observes, making sure that all the students are absorbing the material. Some exercises are more advanced to prevent boredom for experienced students. The majority are designed to be solved in a short time and test and polish your knowledge. Some are more challenging, but none present major challenges. (Presumably, you’ll find those on your own—or more likely they’ll find you).

There are two multimedia CDs associated with this book. The first is bound into the book itself: Thinking in C, described at the end of the preface, which prepares you for the book by bringing you up to speed on the necessary C syntax you need to be able to understand Java.

A second Multimedia CD ROM is available, which is based on the contents of the book. This CD ROM is a separate product and contains the entire contents of the week-long “Hands-On Java” training seminar. This is more than 15 hours of lectures that I have recorded, synchronized with hundreds of slides of information. Because the seminar is based on this book, it is an ideal accompaniment.

The CD ROM contains all the lectures (with the important exception of personalized attention!) from the five-day full-immersion training seminars. We believe that it sets a new standard for quality.

The Hands-On Java CD ROM is available only by ordering directly from the Web site www.BruceEckel.com.

All the source code for this book is available as copyrighted freeware, distributed as a single package, by visiting the Web site www.BruceEckel.com. To make sure that you get the most current version, this is the official site for distribution of the code and the electronic version of the book. You can find mirrored versions of the electronic book and the code on other sites (some of these sites are found at www.BruceEckel.com), but you should check the official site to ensure that the mirrored version is actually the most recent edition. You may distribute the code in classroom and other educational situations.

The primary goal of the copyright is to ensure that the source of the code is properly cited, and to prevent you from republishing the code in print media without permission. (As long as the source is cited, using examples from the book in most media is generally not a problem.)

In each source code file you will find a reference to the following copyright notice:

You may use the code in your projects and in the classroom (including your presentation materials) as long as the copyright notice that appears in each source file is retained.

In the text of this book, identifiers (function, variable, and class names) will be set in bold. Most keywords will also be set in bold, except for those keywords that are used so much that the bolding can become tedious, such as “class.”

I use a particular coding style for the examples in this book. This style follows the style that Sun itself uses in virtually all of the code you will find at its site (see http://java.sun.com/docs/codeconv/index.html), and seems to be supported by most Java development environments. If you’ve read my other works, you’ll also notice that Sun’s coding style coincides with mine—this pleases me, although I had nothing to do with it. The subject of formatting style is good for hours of hot debate, so I’ll just say I’m not trying to dictate correct style via my examples; I have my own motivation for using the style that I do. Because Java is a free-form programming language, you can continue to use whatever style you’re comfortable with.

The programs in this book are files that are included by the word processor in the text, directly from compiled files. Thus, the code files printed in the book should all work without compiler errors. The errors that should cause compile-time error messages are commented out with the comment //! so they can be easily discovered and tested using automatic means. Errors discovered and reported to the author will appear first in the distributed source code and later in updates of the book (which will also appear on the Web site www.BruceEckel.com).

I generally rely on the Sun implementation of Java as a reference when determining whether behavior is correct.

Over time, Sun has released three major versions of Java: 1.0, 1.1 and 2 (which is called version 2 even though the releases of the JDK from Sun continue to use the numbering scheme of 1.2, 1.3, 1.4, etc.). Version 2 seems to finally bring Java into the prime time, in particular where user interface tools are concerned. This book focuses on and is tested with Java 2, although I do sometimes make concessions to earlier features of Java 2 so that the code will compile under Linux (via the Linux JDK that was available at this writing).

If you need to learn about earlier releases of the language that are not covered in this edition, the first edition of the book is freely downloadable at www.BruceEckel.com and is also contained on the CD that is bound in with this book.

One thing you’ll notice is that, when I do need to mention earlier versions of the language, I don’t use the sub-revision numbers. In this book I will refer to Java 1.0, Java 1.1, and Java 2 only, to guard against typographical errors produced by further sub-revisioning of these products.

My company provides five-day, hands-on, public and in-house training seminars based on the material in this book. Selected material from each chapter represents a lesson, which is followed by a monitored exercise period so each student receives personal attention. The audio lectures and slides for the introductory seminar are also captured on CD ROM to provide at least some of the experience of the seminar without the travel and expense. For more information, go to www.BruceEckel.com.

My company also provides consulting, mentoring and walkthrough services to help guide your project through its development cycle—especially your company’s first Java project.

No matter how many tricks a writer uses to detect errors, some always creep in and these often leap off the page for a fresh reader.

There is an error submission form linked from the beginning of each chapter in the HTML version of this book (and on the CD ROM bound into the back of this book, and downloadable from www.BruceEckel.com) and also on the Web site itself, on the page for this book. If you discover anything you believe to be an error, please use this form to submit the error along with your suggested correction. If necessary, include the original source file and note any suggested modifications. Your help is appreciated.

The cover of Thinking in Java is inspired by the American Arts & Crafts Movement, which began near the turn of the century and reached its zenith between 1900 and 1920. It began in England as a reaction to both the machine production of the Industrial Revolution and the highly ornamental style of the Victorian era. Arts & Crafts emphasized spare design, the forms of nature as seen in the art nouveau movement, hand-crafting, and the importance of the individual craftsperson, and yet it did not eschew the use of modern tools. There are many echoes with the situation we have today: the turn of the century, the evolution from the raw beginnings of the computer revolution to something more refined and meaningful to individual persons, and the emphasis on software craftsmanship rather than just manufacturing code.

I see Java in this same way: as an attempt to elevate the programmer away from an operating-system mechanic and toward being a “software craftsman.”

Both the author and the book/cover designer (who have been friends since childhood) find inspiration in this movement, and both own furniture, lamps, and other pieces that are either original or inspired by this period.

The other theme in this cover suggests a collection box that a naturalist might use to display the insect specimens that he or she has preserved. These insects are objects, which are placed within the box objects. The box objects are themselves placed within the “cover object,” which illustrates the fundamental concept of aggregation in object-oriented programming. Of course, a programmer cannot help but make the association with “bugs,” and here the bugs have been captured and presumably killed in a specimen jar, and finally confined within a small display box, as if to imply Java’s ability to find, display, and subdue bugs (which is truly one of its most powerful attributes).

Thanks to the Doyle Street Cohousing Community for putting up with me for the two years that it took me to write the first edition of this book (and for putting up with me at all). Thanks very much to Kevin and Sonda Donovan for subletting their great place in gorgeous Crested Butte, Colorado for the summer while I worked on the book. Also thanks to the friendly residents of Crested Butte and the Rocky Mountain Biological Laboratory who made me feel so welcome.

Thanks to Claudette Moore at Moore Literary Agency for her tremendous patience and perseverance in getting me exactly what I wanted.

My first two books were published with Jeff Pepper as editor at Osborne/McGraw-Hill. Jeff appeared at the right place and the right time at Prentice-Hall and has cleared the path and made all the right things happen to make this the most pleasant publishing experience I’ve ever had. Thanks, Jeff—it means a lot to me.

I’m especially indebted to Gen Kiyooka and his company Digigami, who graciously provided my Web server for the first several years of my presence on the Web. This was an invaluable learning aid.

Thanks to Cay Horstmann (co-author of Core Java, Prentice Hall, 2000), D’Arcy Smith (Symantec), and Paul Tyma (co-author of Java Primer Plus, The Waite Group, 1996), for helping me clarify concepts in the language.

Thanks to people who have spoken in my Java track at the Software Development Conference, and students in my seminars, who ask the questions I need to hear in order to make the material more clear.

Special thanks to Larry and Tina O’Brien, who helped turn my seminar into the original Hands-On Java CD ROM. (You can find out more at www.BruceEckel.com.)

Lots of people sent in corrections and I am indebted to them all, but particular thanks go to (for the first edition): Kevin Raulerson (found tons of great bugs), Bob Resendes (simply incredible), John Pinto, Joe Dante, Joe Sharp (all three were fabulous), David Combs (many grammar and clarification corrections), Dr. Robert Stephenson, Franklin Chen, Zev Griner, David Karr, Leander A. Stroschein, Steve Clark, Charles A. Lee, Austin Maher, Dennis P. Roth, Roque Oliveira, Douglas Dunn, Dejan Ristic, Neil Galarneau, David B. Malkovsky, Steve Wilkinson, and a host of others.

Prof. Ir. Marc Meurrens put in a great deal of effort to publicize and make the electronic version of the first edition of the book available in Europe.

There have been a spate of smart technical people in my life who have become friends and have also been both influential and unusual in that they do yoga and practice other forms of spiritual enhancement, which I find quite inspirational and instructional. They are Kraig Brockschmidt, Gen Kiyooka, and Andrea Provaglio, (who helps in the understanding of Java and programming in general in Italy, and now in the United States as an associate of the MindView team).

It’s not that much of a surprise to me that understanding Delphi helped me understand Java, since there are many concepts and language design decisions in common. My Delphi friends provided assistance by helping me gain insight into that marvelous programming environment. They are Marco Cantu (another Italian—perhaps being steeped in Latin gives one aptitude for programming languages?), Neil Rubenking (who used to do the yoga/vegetarian/Zen thing until he discovered computers), and of course Zack Urlocker, a long-time pal whom I’ve traveled the world with.

My friend Richard Hale Shaw’s insights and support have been very helpful (and Kim’s, too). Richard and I spent many months giving seminars together and trying to work out the perfect learning experience for the attendees. Thanks also to KoAnn Vikoren, Eric Faurot, Marco Pardi, and the rest of the cast and crew at MFI. Thanks especially to Tara Arrowood, who re-inspired me about the possibilities of conferences.

The book design, cover design, and cover photo were created by my friend Daniel Will-Harris, noted author and designer (www.Will-Harris.com), who used to play with rub-on letters in junior high school while he awaited the invention of computers and desktop publishing, and complained of me mumbling over my algebra problems. However, I produced the camera-ready pages myself, so the typesetting errors are mine. Microsoft^® Word 97 for Windows was used to write the book and to create camera-ready pages. The body typeface is Georgia and the headlines are in Verdana. The cover typeface is ITC Rennie Mackintosh.

Thanks to the vendors who created the compilers: Borland, the Blackdown group (for Linux), and of course, Sun.

A special thanks to all my teachers and all my students (who are my teachers as well). The most fun writing teacher was Gabrielle Rico (author of Writing the Natural Way, Putnam, 1983). I’ll always treasure the terrific week at Esalen.

The supporting cast of friends includes, but is not limited to: Andrew Binstock, Steve Sinofsky, JD Hildebrandt, Tom Keffer, Brian McElhinney, Brinkley Barr, Bill Gates at Midnight Engineering Magazine, Larry Constantine and Lucy Lockwood, Greg Perry, Dan Putterman, Christi Westphal, Gene Wang, Dave Mayer, David Intersimone, Andrea Rosenfield, Claire Sawyers, more Italians (Laura Fallai, Corrado, Ilsa, and Cristina Giustozzi), Chris and Laura Strand, the Almquists, Brad Jerbic, Marilyn Cvitanic, the Mabrys, the Haflingers, the Pollocks, Peter Vinci, the Robbins Families, the Moelter Families (and the McMillans), Michael Wilk, Dave Stoner, Laurie Adams, the Cranstons, Larry Fogg, Mike and Karen Sequeira, Gary Entsminger and Allison Brody, Kevin Donovan and Sonda Eastlack, Chester and Shannon Andersen, Joe Lordi, Dave and Brenda Bartlett, David Lee, the Rentschlers, the Sudeks, Dick, Patty, and Lee Eckel, Lynn and Todd, and their families. And of course, Mom and Dad.

Thanks to those who helped me rewrite the examples to use the Swing library: Jon Shvarts, Thomas Kirsch, Rahim Adatia, Rajesh Jain, Ravi Manthena, Banu Rajamani, Jens Brandt, Nitin Shivaram, and everyone who expressed support. This really helped me jump-start the project.