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From: Eric Sosman <esosman@comcast-dot-net.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: optimsed HashMap
Date: Mon, 26 Nov 2012 20:28:08 -0500
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On 11/26/2012 6:44 PM, Daniel Pitts wrote:
> On 11/23/12 5:12 PM, Roedy Green wrote:
>> Is there something like HashMap but that optimised when nearly always
>> the thing you are looking up is not in the list, and when you can add
>> the list of words to look up and then freeze it.
>>
>> I have to scan an entire website looking up every word.
>>
>
> I don't think your use-case needs this kind of (read "micro")
> optimization.  However, I have often wished for a way to get a Map.Entry
> for a key, which could then be used to insert a new value efficiently.
>
> Map.Entry<K,V> getOrAddEntry(K key);
>
>
> Map.Entry<K,V> e = map.getOrAddEntry(myKey);
>
> if (e.getValue() == null) {
>     e.setValue(newValue(myKey));
> }
>
> useValue(e.getValue());
>
> Alas, not exactly possible to add it now.

     java.util.concurrent.ConcurrentMap has putIfAbsent().

-- 
Eric Sosman
esosman@comcast-dot-net.invalid