Re: optimsed HashMap
On 11/26/12 5:28 PM, Eric Sosman wrote:
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().
putIfAbsent isn't exactly what I want. First, I might not want to go to
the expense of creating a new value *unless* there isn't already one.
Second, this is an operation that may not need the overhead of a
concurrency-safe map.
The first problem *can* be overcome by using a wrapper object, but that
adds additional overhead, and the point of this is to reduce overhead.