Denis Kishenko 写道:
Let's continue discussion about hashCode() from thread "Algorithmic
tricks".
2006/7/27, Spark Shen <[EMAIL PROTECTED]>:
I do have a concern that in some classes, hash calculation does have
very import impact, but in some others may not be so important, or
may not
be taken so heavy use. IMHO, the 'degree of hashing' provided by this
method may be a little too general to use by all classes. It may be too
heave
for some, but too light for others.
Please give some examples of heavy and light hashing in your vision.
According to spec, lots of the classes do not override hashCode method,
which gives a hint that these classes do not need.
And many class say explicitly that 'Returns the standard hash code as
defined by the ||Object.hashCode()|
<cid:[email protected]>| method.'
Cited from java.lang.Character.hashCode(). Although this class has many
internal member variable, may be its not necessary
to recalculate it's hashCode. Under this situation, the method seems a
little heavy.
And following is cited from java.util.Locale.hashCode()
'Override hashCode. Since Locales are often used in hashtables, caches
the value for speed.'
This is a hint that the more Locales are dispersed the better, may be
its a little to light using a standard hash algorithm here.
Correct me if I am wrong.
> But only several classes are using it. I suggest integrate HashCode in
> all hashCode() implementations (about 200 files), I can do this.
Anybody
> else can improve HashCode work.
>
Such a utility class is very helpful, but utilize it in all classes may
not be suitable. And do have some 'premature optimization' smell here.
As anthon said
"What I'm talking about is not related to 'premature optimization' that
is now being discussed in another thread but something very narrow,
limited to maybe one method and not influencing anything else. "
So your suggestion is leave hashCode as is?
IMHO, if there is no test cases to prove that some hash code
implementation is 'Bad', may be its too early to substitute them all.
Best regards
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Spark Shen
China Software Development Lab, IBM
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