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Re: Something Better than ArrayList

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On Tue, 21 Jun 2011, Gene Wirchenko wrote:

> On Tue, 21 Jun 2011 02:22:46 -0700 (PDT), Paul Cager
> <paul.cager@googlemail.com> wrote:
>
>> On Jun 21, 6:34 am, Gene Wirchenko <ge...@ocis.net> wrote:
>>> Dear Java'ers:
>>>      The name of the class is what I need.  I assume I can find the
>>> docs once I know what it is called.
>>
>> Others have already pointed you to java.util.Map, which answers your
>> immediate question. You might also want to have a look at the Java
>> "Collections" tutorial for more general information:
>> http://download.oracle.com/javase/tutorial/collections/index.html
>
>     I found it rather dry, but did manage to write a proof-of-concept
> program for a symbol table.  However, I have to check for duplication
> before put()ing.  Is there a way to combine a Map and a Set to avoid
> this?
>
>     For the Map
>
>   static Map<String,String> SymbolTable=new HashMap<String,String>();
>
> I would like to write something like
>
>   static boolean TryToAdd
>    (
>    String theKey,
>    String theData
>    )
>      {
>      return SymbolTable.put(theKey,theData);
>      }
>
> instead of
>
>   static boolean TryToAdd
>    (
>    String theKey,
>    String theData
>    )
>      {
>      if (SymbolTable.containsKey(theKey))
>         return false;
>      else
>         {
>         SymbolTable.put(theKey,theData);
>         return true;
>         }
>      }
>
>     Am I missing something or is this not supported?

You can't do it with a normal Map. You can do it with a ConcurrentMap:

http://download.oracle.com/javase/6/docs/api/java/util/concurrent/ConcurrentMap.html

ConcurrentMap has it because you can't easily build an efficient 
threadsafe implementation of putIfAbsent on top of the normal Map 
interface. It's a bit of a shame Map doesn't have it, because it's useful 
even if you're not dealing with multiple threads!

tom

-- 
No man ever steps in the same river twice, for it's not the same river
and he's not the same man. -- Heraclitus

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Something Better than ArrayList Gene Wirchenko <genew@ocis.net> - 2011-06-20 22:34 -0700
  Re: Something Better than ArrayList Donkey Hottie <donkey@fredriksson.dy.fi> - 2011-06-21 09:55 +0300
    Re: Something Better than ArrayList Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-21 09:00 +0000
      Re: Something Better than ArrayList Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-06-21 10:48 +0000
        Re: Something Better than ArrayList Tom Anderson <twic@urchin.earth.li> - 2011-06-21 22:57 +0100
  Re: Something Better than ArrayList Paul Cager <paul.cager@googlemail.com> - 2011-06-21 02:22 -0700
    Re: Something Better than ArrayList Gene Wirchenko <genew@ocis.net> - 2011-06-21 14:19 -0700
      Re: Something Better than ArrayList Tom Anderson <twic@urchin.earth.li> - 2011-06-21 22:56 +0100
        Re: Something Better than ArrayList Gene Wirchenko <genew@ocis.net> - 2011-06-21 16:39 -0700
  Re: Something Better than ArrayList Gene Wirchenko <genew@ocis.net> - 2011-06-21 07:51 -0700

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