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

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On 8/31/12 3:26 AM, Andreas Leitgeb wrote:
> Robert Klemme <shortcutter@googlemail.com> wrote:
>> On 30.08.2012 23:55, Andreas Leitgeb wrote:
>>> Daniel Pitts <newsgroup.nospam@virtualinfinity.net> wrote:
>>>> Or, if you know all the keys before hand, you can use instead
>>>>   Map<Long,MyLongWrapper> map.
>>>> MyLongWrapper would have .set() and .get(), or even .actUpon()
>>>> depending on the semantics you need.
>
> My code now looks essentially like this: (containing class omitted)
>
>    void doSomething() {
>       // Val could be a static nested or a toplevel class, as well
>       //  I've got it here for local context. I'd separate it out
>       //  only if profiling results suggested doing so. ;-)
>       final class Val {
>          private long val=0; long getVal() { return val; }
>          void actUpon(long arg) { val = some_formula_on_val_and_arg; }
>       }
>       Map<Long,Val> map = new HashMap<Long,Val>()
>       for (Long key : listOfInterestingKeys) { map.put(key,new Val()); }
>
>       // the main iteration: (each foo has two keys and a value)
>       for (Foo foo : fooCollection) { Val fw;
>          fw=map.get( foo.key1 ); if (fw != null) fw.actUpon(foo.value);
>          fw=map.get( foo.key2 ); if (fw != null) fw.actUpon(foo.value);
>          // plus some more stuff using also the "uninteresting" keys.
>       }
>       for (Map.Entry<Long,Val> me : map.entrySet() ) {
>          doSomething(me.getKey(),me.getValue().getVal());
>       }
>    }
>
> Again: thanks, Daniel Pitts, for pointing me the right direction
> with a mutable value-wrapper class, instead of some Entry-alike!
>
>> containsKey() is unnecessary work.  Just get(), and if it's null [...]
>
> Was indeed. And my action for null happened to be "ignore".
>
>> Btw, if you use long as member instead of Long then you do not even
>> necessarily have more objects.
>
> While that happened to apply to my case, it wasn't really a primary concern.
>
The real reason IMHO to use "long" over "Long", is that Long can be 
null, and sometimes that just doesn't make any sense semantically. The 
fact that it tends to be faster and use less memory is just a benefit.

Same goes for all primitives vs primitive wrappers.

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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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