Java Puzzlers

Kylar writes "When you have spare time and decide to do something with a book (That's like an analog webpage, for the neuronauts among us), how often do you turn to a computer related book? How often has it happened in the last year? Right. The problem being that computer books are often either: a) boring, b) difficult to read, c) poorly written, or possibly: d) made of cheese." Read on for the rest of Kylars' review. Traps, Pitfalls, and Corner Cases - Java Puzzlers author Joshua Bloch, Neal Gafter pages 282 publisher Addison-Wesley rating 9 out of 10 reviewer Tom Byrne ISBN 0-321-33678-X summary 95 Corner cases and traps that any serious java developer should be aware of (or entertained by.)

Java Puzzlers is none of the above(*), being well written, amusing, whimsical, and above all, informative. Bloch and Gafter have brought us a book that entertains us with corner-cases, one-in-a-million chances and other happenings that explore the ins, outs, and guts of the Java Programming Language.

Anyone who has been a serious java programmer in the last several years should know the name Josh Bloch, and more importantly, should have read his book Effective Java. Josh, acting as java's platform architect has been directing and guiding Java into it's current incarnation as a mature, robust (Cue the laughter from the peanut gallery) programming language.

This book primarily references the Java 1.5 programming language, and some of the puzzles are 1.5-specific, although a significant portion of the problems are applicable to previous versions. Also, this book is aimed towards people who are competent-to-expert java programmers, and although there is a lot of good information, people who are new to Java will probably be a bit lost. As it stands, I have 7 years of Java experience, and I was only able to figure out about 15% of the puzzles without resorting to code, or more frequently the answer. The reason that I didn't stop to try out most of these problems is that the book is eminently readable, and difficult to put down (unusual for a computer book, and doubly so for one that delves deeply into a language specification document.)

This book dives into a lot of esoteric bits of the Java Language Specification, also known as "The Big Paper That Sometimes Tells Us Why Java Acts Like That," and there are lots of bits in there that don't even make sense, let alone seem intuitive.

Divided into 10 parts, each part presents a series of different code problems that usually present a small method or class that looks innocuous, but in reality exposes a piece of behavior that is strange, spectacular, or, more often, completely confusing. The book exposes flaws in the language, including one of my personal pet peeves, their inability to have a consistent Date object, and this is noted in Puzzle 62 by my favorite line in the book: "The lesson for API designers is: If you can't get it right the first time, at least get it right the second..."

One topic that I found was a continually recurring theme had to do with handling primitives and what happens when they are cast into different types. Java provides a lot of ways to deal with primitives, and for the most part, they play nicely with each other. There are several occurrences that really surprised me. A perfect example is the following innocent statements:

byte b = -1;
char c = (char)b;

so c=-1, right? Wrong. Places like this are things that you could potentially knock your head against the wall trying to figure out why something doesn't do what it appears to do.
(In this case, byte is signed, char isn't, and the widening cast fills in bits, leaving c=65535.)

A good job is also done describing best-practices for API and library designers, as well as us, the more mundane programmers.

The only downside (from my background and point of view - that of an applications architect, and not generally as a language or API designer) - is that some of the amazing optical illustrations can cause dizziness and nausea - although I can't guarantee that won't happen by the loops and twists that your mind will be tied into because of the puzzles.

Lastly, Bloch & Gafter include an appendix that serves as a summary to all the pitfalls and traps that are introduced in the book, and almost could be an appendix to Bloch's 'Effective Java'.

The bottom line is that in reading this book I learned a fair amount about several edge cases and issues that I had actually encountered - and it increased my understanding as to HOW java does things - although I'm fairly certain that I'll never understand the WHY. And most of all - I enjoyed this book, from start to finish, and that's rare, and worth the time.

You can purchase Java Puzzlers from bn.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.

Comments

master of the obvious

[hometoast]

byte b = -1;
char c = (char)b;
so c=-1, right? Wrong. Places like this are things that you could potentially knock your head against the wall trying to figure out why something doesn't do what it appears to do.
(In this case, byte is signed, char isn't, and the widening cast fills in bits, leaving c=65535.)

That's not expected??

Re:master of the obvious

[AKAImBatman]

Amen. The Java Language Specification states that char IS NOT A NUMBER. It's a character representation and should be treated as such. Thus the entire example is contrived, and makes no sense. It *might* be interesting from the perspective of loading a file (e.g. buffer.append((char)in.read());), except that the IO streams provide Integers to get around the sign problem.

This is why in computer science they have a term for supposed "idiosyncracies" like this: "Garbage In Garbage Out" (GIGO)

Re:garbage collector

[Azarael]

I doubt that most experienced programmers would get hung up over the byte b example. I'm pretty sure that you'd get similar behaviour with C and a lot of other languages.

Kind of

[brunes69]

See, to a C coder, this is non-obvious because both the types would be signed, and if you wanted it unsigned you would have to say so.

It has always diven me nuts how Java forces its own signed-ness on it's primitives. The fact that you can't have an unsigned int in Java 1.5 is a huge pain, because it is not like it is simpler to just use char everywhere, since then you lose all the autoboxing capability of Integer/int. So, you have to deal with it yourself. It's a big mistake IMO.

Re:Kind of

[codegen]

See, to a C coder, this is non-obvious because both the types would be signed, and if you wanted it unsigned you would have to say so.

Sigh... Not true. Wether chars default to signed or unsigned is vendor specific in the ANSI C spec. If you code depends on chars being signed or not then you have to state it explicitly if you want your code to be portable. I have been bitten by this on one important occasion when I was still in Industry and have never forgotten it.

Thats the whole point of the "puzzler"

[brunes69]

It is to expose a flaw in the language.

Why should a primitive byte be signed, but not a primitive char?

And why can't I have an unsigned int primitive in Java?

Primitives in Java are a real pain to work with compared to most languages.

Re:Thats the whole point of the "puzzler"

[$RANDOMLUSER]

> Why should a primitive byte be signed, but not a primitive char?

Because a byte is a numeric class, and a char is a character class? Your question is like asking why booleans can't be signed or unsigned.

Re:Thats the whole point of the "puzzler"

[kaffiene]

>Primitives in Java are a real pain to work with compared to most languages.

Bullshit. I've coded through asm, c, c++, java and they all have their own ways of doing things which you need to be aware of. The language is NOT the problem.

Re:Puzzling indeed

[$RANDOMLUSER]

1) Code readability.
2) Speed of development.
3) Lack of "cute" features that break easily.
4) Javadoc!!
5) Bazillions of pre-written, pre-tested source-available library functions.

Because characters aren't numbers.

[MS-06FZ]

I think the whole notion of a "character" type being assigned a numerical value is dubious in the first place. That's not to say the idea of a character coding that translates between characters and numbers isn't sensible, but the character itself is not a number - it's a character. I like Python's approach to the solution - there simply is no "atomic" character type (defining such a thing when character sets have characters that aren't uniform size is questionable anyway)

So given that characters aren't numbers, is it really so hard to imagine that people see that code and can't readily guess what sort of number a character is? I guess one could say that the character set is indexed with non-negative integers, so the character type should be non-negative - but a logical derivation isn't the same as a plain fact, and other languages aren't so sensible in those kinds of decisions...

Java puzzles? I do them everyday

[helix_r]

Unfortunately, real-life java problems are never very interesting.

Invariably the solution consists of editing an annoying xml config file, or perhaps correcting one of my daily misconceptions about some boring detail in whatever convoluted j2ee framework I am forced to work with.

Re:Java puzzles? I do them everyday

[Decaff]

Unfortunately, real-life java problems are never very interesting.

Virtually all real-life coding problems are uninteresting. It is nothing to do with Java.

Code books in general?

[RingDev]

Why bother? I have 1 HTML/CSS book I keep on hand just because I've used it so much. Everything else, I use google. Its faster (for me) to find designs, references, and code samples online then it is for me to get a book, look up the index and flip through the pages. I even gave up on my old SQL bible as Google can get me syntax and samples faster then I can find them in the book.

-Rick

Re:Code books in general?

[ForumTroll]

The tutorials and code samples that are online are often trivial when compared to the in depth detail that you will find in a good book. Also, they're often out of date and some what misinformed. Don't get me wrong, I've done a lot of research online and lots of the information was very well presented and put together however I don't think I've ever seen a tutorial or paper that is as good or equivalent to some of the professionally written books available. I also hate reading large books or tutorials online. Perhaps, it's just a personal preference of mine.

On a side note, if I had something that was small and lightweight I would probably start using http://safari.oreilly.com/">Safari Bookshelf. For several reasons, I just can't seem to enjoyably read an entire books worth of information sitting at my desk reading off a monitor.

Missing Option

[Anonymous Coward]

Most technical books are: ...

E) Out of date before the ink is dry.

disappointed -- try the java cert exam

[SamSeaborn]

I was excited when I saw the "Java Puzzlers" subject heading. But that byte to char example left me under-whelmed.

Have any other more interesting/fun examples?

If you want some puzzlers, look for copies of the Sun Java Programmer certification exam. There's lots of "we're not testing to see if you're a good programmer, just testing to see if you can find the unexpected result in the insanity-pepper code" snippets there.

boxlight

Re:disappointed -- try the java cert exam

[mmusson]

I enjoy obscure code examples as an antidote to drinking the Java is perfect Koolaid. Examples like:

   private int foo()
   {
      try
      {
         return 0;
      }
      finally
      {
         return 1;
      }
   }

Re:disappointed -- try the java cert exam

[Anonymous Coward]

Ummm.... Fire your whole team.

a char with a value of 65535?

[poot_rootbeer]

(In this case, byte is signed, char isn't, and the widening cast fills in bits, leaving c=65535.)

char

, being a character datatype, shouldn't have its value expressed as an integer.

The correct value of

c

is the glyph or other character corresponding to entry 65535 in whatever character encoding Java is currently using. (Assuming UCS-2, it's an invalid codepoint and therefore undefined.)

Yes, for purposes of demonstrating that

int

is stored as a signed value and

char

isn't the example is correct, but that's still a little more of an under-the-hood mentality that's more appropriate to C than to Java.

Re:a char with a value of 65535?

[Anonymous Coward]

"but that's still a little more of an under-the-hood mentality that's more appropriate to C than to Java."

Wrong, wrong, wrong...

This should be something all developers understand about the language they are using. Not knowing or considering it "out of scope" for the language is ridiculous and can cause some nasty logic bugs in the code.

It appropriate for any language that supports up/down casting of primitives... (not to be confused with type conversion such as string to int and int to string in PHP or Perl)

Oh come on!

[Xarius]

Kylar writes "When you have spare time and decide to do something with a book (That's like an analog webpage, for the neuronauts among us), how often do you turn to a computer related book? How often has it happened in the last year? Right. The problem being that computer books are often either: a) boring, b) difficult to read, c) poorly written, or possibly: d) made of cheese. Read on for the rest of Kylars' review.

I know slashdot is hardly the pinnacle of good reporting, but that summary is bordering on the idiotic. Were those daft little bits of meaningless fluffy non-humour put in there simply to up the word count?

Re:garbage collector

[Heembo]

> When we moved into millions of cycles per second (big big solaris servers) we had similar problems...

When we use big servers, Java 1.5, huge centralized clusters (offsite backup!), connection pooling, application level caching, big Oracle clusters, and pro (expensive) app servers (no tomcat) not only can we handle millions of cycles, we can handle a lot, lot, lot more at 6 sigma reliability and better.

I'm guessing your problem is a deeper architectural issue, not a "bug with Java".

Re:garbage collector

[bryanmanwaring]

It never ceases to amaze me how naive people can be when it comes to Java. The truth is, the underlying VM is a different technology than the "Manage it yourself" tradition of C/C++. While garbage collection is an additional process that occurs in a VM environment such as Java or .NET, there are peformance advantages to using such a process. (And no, I am not refering to the programmer laziness argument about not having to manage memory in Java... I am talking about the efficiency of allocation and deallocation that a Java VM affords)

I do not plan on engaging in any arguments back and forth about the two types of memory management... But if you are truly interested in an article that means to show the reality of the "performance characteristics" of a Java VM, please read the article listed below. It is truly a well written article and worth the read.

http://www-128.ibm.com/developerworks/java/library /j-jtp09275.html?ca=dgr-lnxw01JavaUrbanLegends

Re:Not interested...in sudoku

[extremely]

If you have a super fast solution to the sudoku puzzle family you should probably write it up. Sudoku is NP-complete... if you've solved it then you've cracked every encryption protocol known to man...