How well do you really know Java? Are you a code sleuth? Have you ever spent
days chasing a bug caused by a trap or pitfall in Java or its libraries? Do
you like brainteasers? Then this is the book for you!
Most of the puzzles take the form of a short program whose behavior isn't what
it seems. Can you figure out what it does? Puzzles are grouped loosely according
to the features they use, and detailed solutions follow each puzzle. The solutions
go well beyond a simple explanation of the program's behavior--they show you
how to avoid the underlying traps and pitfalls for good. A handy catalog of
traps and pitfalls at the back of the book provides a concise taxonomy for future
reference. Solve these puzzles and you'll never again fall prey to the counterintuitive
or obscure behaviors that can fool even the most experienced programmers.
Preface
"Like many books, this one had a long gestation period. We've collected Java
puzzles for as long as we've worked with the platform: since mid-1996, in case
you're curious. In early 2001, we came up with the idea of doing a talk consisting
entirely of Java puzzles. We pitched the idea to Larry Jacobs, then at Oracle,
and he bought it hook, line, and sinker.
We gave the first "Java Puzzlers" talk at the Oracle Open World conference
in San Francisco in November 2001. To add a bit of pizazz, we introduced ourselves
as "Click and Hack, the Type-it Brothers" and stole a bunch of jokes
from Tom and Ray Magliozzi of Car Talk fame. The presentation was voted best-in-show,
and probably would have been even if we hadn't voted for ourselves. We knew
we were on to something.
Dressed in spiffy blue mechanic's overalls emblazoned with the "cup and
steam" Java logo, we recycled the Oracle talk at JavaOne 2002 to rave reviews--at
least from our friends. In the years that followed, we came up with three more
"Java Puzzlers" talks and presented them at countless conferences,
corporations, and colleges in cities around the globe, from Oslo to Tokyo. The
talks were almost universally well liked, and we got very little fruit thrown
at us. In the March 2003 issue of Linux Magazine, we published an article consisting
entirely of Java puzzles and received almost no hate mail. This book contains
nearly all the puzzles from our talks and articles and many, many more.
Although this book draws attention to the traps and pitfalls of the Java platform,
we do not mean to denigrate it in any way. It is because we love the Java platform
that we've devoted nearly a decade of our professional lives to it. Every platform
with enough power to do real work has some problems, and Java has far fewer
than most. The better you understand the problems, the less likely you are to
get hurt by them, and that's where this book comes in.
Most of the puzzles in the book focus on short programs that appear to do one
thing but actually do something else. That's why we've chosen to decorate the
book with optical illusions--drawings that appear to be one thing but are actually
another. Also, you can stare at them while you're trying to figure out what
in the world the programs do.
Above all, we wanted this book to be fun. We sincerely hope that you enjoy
solving the puzzles as much as we enjoyed writing them and that you learn as
much from them as we did.
And by all means, send us your puzzlers! If you have a puzzle that you think
belongs in a future edition of this book, write it on the back of a $20 bill
and send it to us, or e-mail it to puzzlers@javapuzzlers.com. If we use your
puzzle, we'll give you credit. Last but not least, don't code like my brother."
Josh Bloch
Neal Gafter
San Jose, California
May 2005
Table of Contents
1. Introduction.
2. Expressive
Puzzlers.
Puzzle 1: Oddity
Puzzle 2: Time for a Change
Puzzle 3: Long Division
Puzzle 4: It's Elementary
Puzzle 5: The Joy of Hex
Puzzle 6: Multicast
Puzzle 7: Swap Meat
Puzzle 8: Dos Equis
Puzzle 9: Tweedledum
Puzzle 10: Tweedledee
3. Puzzlers
with Character.
Puzzle 11: The Last Laugh
Puzzle 12: ABC
Puzzle 13: Animal Farm
Puzzle 14: Escape Rout
Puzzle 15: Hello Whirled
Puzzle 16: Line Printer
Puzzle 17: Huh?
Puzzle 18: String Cheese
Puzzle 19: Classy Fire
Puzzle 20: What's My Class?
Puzzle 21: What's My Class, Take 2
Puzzle 22: Dupe of URL
Puzzle 23: No Pain, No Gain
4. Loopy
Puzzlers.
Puzzle 24: A Big Delight in Every Byte
Puzzle 25: Inclement Increment
Puzzle 26: In the Loop
Puzzle 27: Shifty i's
Puzzle 28: Looper
Puzzle 29: Bride of Looper
Puzzle 30: Son of Looper
Puzzle 31: Ghost of Looper
Puzzle 32: Curse of Looper
Puzzle 33: Looper Meets the Wolfman
Puzzle 34: Down for the Count
Puzzle 35: Minute by Minute
5. Exceptional
Puzzlers.
Puzzle 36: Indecision
Puzzle 37: Exceptionally Arcane
Puzzle 38: The Unwelcome Guest
Puzzle 39: Hello, Goodbye
Puzzle 40: The Reluctant Constructor
Puzzle 41: Field and Stream
Puzzle 42: Thrown for a Loop
Puzzle 43: Exceptionally Unsafe
Puzzle 44: Cutting Class
Puzzle 45: Exhausting Workout
6. Classy
Puzzlers.
Puzzle
46: The Case of the Confusing Constructor
Puzzle 47: Well, Dog My Cats!
Puzzle 48: All I Get Is Static
Puzzle 49: Larger Than Life
Puzzle 50: Not Your Type
Puzzle 51: What's the Point?
Puzzle 52: Sum Fun
Puzzle 53: Do Your Thing
Puzzle 54: Null and Void
Puzzle 55: Creationism
7. Library
Puzzlers.
Puzzle 56: Big Problem
Puzzle 57: What's in a Name?
Puzzle 58: Making a Hash of It
Puzzle 59: What's the Difference?
Puzzle 60: One-Liners
Puzzle 61: The Dating Game
Puzzle 62: The Name Game
Puzzle 63: More of the Same
Puzzle 64: The Mod Squad
Puzzle 65: A Strange Saga of a Suspicious Sort
8. Classier
Puzzlers.
Puzzle 66: A Private Matter
Puzzle 67: All Strung Out
Puzzle 68: Shades of Gray
Puzzle 69: Fade to Black
Puzzle 70: Package Deal
Puzzle 71: Import Duty
Puzzle 72: Final Jeopardy
Puzzle 73: Your Privates Are Showing
Puzzle 74: Identity Crisis
Puzzle 75: Heads or Tails?
9. More Library
Puzzlers.
Puzzle 76: Ping Pong
Puzzle 77: The Lock Mess Monster
Puzzle 78: Reflection Infection
Puzzle 79: It's a Dog's Life
Puzzle 80: Further Reflection
Puzzle 81: Charred Beyond Recognition
Puzzle 82: Beer Blast
Puzzle 83: Dyslexic Monotheism
Puzzle 84: Rudely Interrupted
Puzzle 85: Lazy Initialization
10. Advanced
Puzzlers.
Puzzle 86: Poison-Paren Litter
Puzzle 87: Strained Relations
Puzzle 88: Raw Deal
Puzzle 89: Generic Drugs
Puzzle 90: It's Absurd, It's a Pain, It's Superclass!
Puzzle 91: Serial Killer
Puzzle 92: Twisted Pair
Puzzle 93: Class Warfare
Puzzle 94: Lost in the Shuffle
Puzzle 95: Just Desserts
Appendix
A: Catalog of Traps and Pitfalls.
Appendix
B: Notes on the Illusions.
References.
Index.
