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Re: Question about HashMap and Map.Entry ...

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Daniel Pitts <newsgroup.nospam@virtualinfinity.net> wrote:
> On 8/30/12 10:46 AM, markspace wrote:
>> On 8/30/2012 10:39 AM, Andreas Leitgeb wrote:
>>> What I'm missing, however, is:
>>>    How would I get the Entry for a given key?
>> What about: [...] I think that's what you said you are doing.
You thought essentially right, markspace ;-)

> In theory, this does more work than it needs to, computing the hash 
> bucket twice,...

That lets it look like I was caring for performance and 
(premature, of course) optimization, which I've indeed
often a weakness for, but which isn't relevant for this
thread.

Let's say, I've got a method that takes an Map.Entry, and
the new value, and it updates the Entry's value accordingly.

So far I happened to use it for all keys in a Map, so 
I iterated the entrySet, and called the method on each
loop-cycle.

Now, I'd rather call that method for specific keys, and
that's how I'd arrive at the outset of this thread.

My choice is now:
a) duplicating the method's code into one that operates
     on the map directly for a key, or inlining the method's
     code directly into the loop-body. (what I did)
b) creating an anonymous "implementation" of Map.Entry
     with key&value, and writing the value back to the
     map unconditionally afterwards. (I don't care about
     eventually overwriting with same value)

but unfortunately not:
c) getting some darned Map-backed Entry just for that
     darned key ;-)

> I would like to suggest to the OP to look into Trove <...>,
> which has support for primitive collections (longs, rather
> than Longs), which may be much faster and more memory efficient,
> depending on your use-cases.

If the TLongLongHashMap had a method to return a
java.util.Map.Entry<Long,Long>, then I'd be all for it ;-)

But it was still interesting to read about adjustOrPutValue(),
foreach*() and putIfAbsent() methods. These might come in handy some
time, and it's good to know, these trove collections offer stuff beyond
merely wrapping the primitives directly, compared to java.util.HashMap.

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Question about HashMap and Map.Entry ... Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-08-30 17:39 +0000
  Re: Question about HashMap and Map.Entry ... markspace <-@.> - 2012-08-30 10:46 -0700
    Re: Question about HashMap and Map.Entry ... Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-08-30 11:15 -0700
      Re: Question about HashMap and Map.Entry ... Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-08-30 19:24 +0000
        Re: Question about HashMap and Map.Entry ... Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-08-30 19:32 +0000
          Re: Question about HashMap and Map.Entry ... Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-08-30 13:08 -0700
            Re: Question about HashMap and Map.Entry ... Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-08-30 21:55 +0000
              Re: Question about HashMap and Map.Entry ... Robert Klemme <shortcutter@googlemail.com> - 2012-08-31 07:27 +0200
                Re: Question about HashMap and Map.Entry ... Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-08-31 10:26 +0000
                Re: Question about HashMap and Map.Entry ... Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-08-31 11:22 -0700
                Re: Question about HashMap and Map.Entry ... Robert Klemme <shortcutter@googlemail.com> - 2012-09-01 11:06 +0200
        Re: Question about HashMap and Map.Entry ... markspace <-@.> - 2012-08-30 14:30 -0700
          Re: Question about HashMap and Map.Entry ... Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-08-30 22:42 +0000
        Re: Question about HashMap and Map.Entry ... markspace <-@.> - 2012-08-30 14:34 -0700
  Re: Question about HashMap and Map.Entry ... Lew <lewbloch@gmail.com> - 2012-08-30 13:42 -0700
    Re: Question about HashMap and Map.Entry ... Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-08-30 22:34 +0000

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