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Re: Question about Effective Java

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On Thursday, February 9, 2012 6:08:51 PM UTC-8, Eric Sosman wrote:
> On 2/9/2012 7:40 PM, Novice wrote:
> > At first glance it seems simple enough; in any other class, "this" refers
> > to an instance of the class that contains the "this", just like we see
> > here. But I'm not used to seeing several methods in a class all return
> > "this".

Get used to it.

Have you considered Googling for "builder pattern"? You might be surprised by 
what just a few minutes of reading can reveal.

>      Analogies are never perfect, but often helpful.  So, imagine a
> group of friends ordering pizza: They've got a slip of paper listing
> possible toppings, and they're going to put check marks next to the
> items they want.  "Pepperoni," says George, "gotta have pepperoni,"
> making his mark on the paper and passing it to Gina.  "Mushrooms
> make my breath fresher," she says, adding her mark and passing the
> paper along to Gail.  She opts for extra cheese and hands the paper
> to Guy, who's worried about his weight and says "Sounds good, let's
> just go with these three."  He passes the paper over the counter to
> Guido, who makes them a pluperfectly personalized pizza.
> 
>      Now, what do the friends pass among themselves during this
> colloquy?  Do they pass the pizza?  No, it hasn't even been made
> yet.  Do they pass their chosen ingredients?  No, George doesn't
> have a handful of pepperoni, nor does Gina have mushrooms nor Gail
> extra cheese, and Guy doesn't have plenty of nothing.  What they
> pass is the slip of paper, the specification of the pizza they would
> like Guido to build for them.
> 
>      ... and that's very much like what's going on with Builder and
> NutritionFacts.  The friends "make marks on" a Builder, then hand
> the Builder to Guido, who makes them a NutritionFacts built to its
> specification.
> 
>      That's the idea; now to the returning of "this".  It's just a
> convenience, really.  Imagine that all those Builder methods were
> "void", returning nothing at all.  Then you'd write
> 
> 	NutritionFacts.Builder b = new NutritionFacts.Builder(300, 4);
> 	b.calories(950);
> 	b.sodium(800);
> 	b.carbohydrate(1025);
> 	NutritionFacts facts = b.build();
> 
> That is, you'd use the variable "b" to hold a reference to the
> Builder while you "make your marks" on it.  Eventually, you call
> its build() method to "hand it to Guido" and get a pizza -- er,
> that is, a NutritionFacts -- made to order.  This would work just
> fine, and there's nothing fundamentally wrong with it.
> 
>      But if each of the Builder method returns a reference to the
> Builder it has just "marked" things can be written a little more
> compactly:
> 
> 	NutritionFacts facts =
> 	    new NutritionFacts.Builder(300, 4)
> 	       .calories(950)
> 	       .sodium(800)
> 	       .carbohydrate(1025)
> 	    .build();
> 
> Observe that you no longer need the "b" variable: The "new" creates
> a Builder and produces a reference to it, the calories() method
> modifies that Builder and returns a reference that the sodium()
> method can use, ..., until eventually the build() method takes all
> the information stored in the Builder and uses it to generate a
> Pizza -- er, that is, a NutritionFacts.  Since there's no "b" to
> refer to the Builder, it becomes eligible for garbage collection
> as soon as its fulfilled its purpose, namely, specifying what's
> wanted in the new NutritionFacts.
> 
>      In short, the returning of "this" enables a convenience, but
> is not truly fundamental to the pattern of using a builder of some
> kind to hold the parameters for a hidden constructor.
> 
> > I'm also not used to named classes nested within classes. (I'm

Read the Java tutorials.

Then study the Java Language Specification (JLS) about "member types".

The keyword is "scope". The scope of a nested class is defined like any other 
class or instance member: 'public', 'protected', package-private or 'private'.
There are also some special rules about access to the enclosing type's members.

> > familiar with anonymous inner classes like window listeners and with

It's the same, but anonymous classes don't have a name (hence "anonymous").

Do note that not all nested classes are inner classes; some are static.

> > putting additional named classes within the same source file in a
> > sequential fashion but putting a named class within another is still
> > feels a little odd.)

"Not familiar", "feels a little odd". Jeez, get over it. You sound like a 
whiney little baby.

If you haven't got the ability to learn new stuff, you won't last 10 minutes in 
software development. Really, get over it.

>      You'll get used to it.  The pattern works even if the builder
> class is completely separate from the built class -- consider, for
> example, StringBuilder and String.  (And note how StringBuilder's
> append() method, for instance, returns a reference to the same
> StringBuilder that the append() modified.)
> 
> > I'll post back if I can't make my peace with this slightly exotic
> > technique ;-)

Why don't you first study up on it? The newsgroup is not a help desk, and it 
certainly is no substitute for study.

And you call it "exotic" only because you're incompletely trained. Don't make
such judgments given your lack of experience. You are in no position yet to 
decide what is "exotic" and what isn't. You need to check your ego at the door.

>      You'll get used to it.  (Is there an echo in here?)

Bottom line: Study, and get used to learning new things.

-- 
Lew

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Question about Effective Java Novice <novice@example..com> - 2012-02-09 17:54 +0000
  Re: Question about Effective Java markspace <-@.> - 2012-02-09 10:39 -0800
    Re: Question about Effective Java Novice <novice@example..com> - 2012-02-10 00:07 +0000
      Re: Question about Effective Java markspace <-@.> - 2012-02-09 16:42 -0800
  Re: Question about Effective Java Patricia Shanahan <pats@acm.org> - 2012-02-09 14:19 -0800
    Re: Question about Effective Java Novice <novice@example..com> - 2012-02-10 00:40 +0000
      Re: Question about Effective Java Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-09 21:08 -0500
        Re: Question about Effective Java Lew <lewbloch@gmail.com> - 2012-02-10 09:01 -0800
  Re: Question about Effective Java "John B. Matthews" <nospam@nospam.invalid> - 2012-02-10 11:59 -0500

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