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I am writing an application where memory, and to a lesser extent speed, are vital. I have found from profiling that I spend a great deal of time in Map and Set operations. While I look at ways to call these methods less, I am wondering whether anyone out there has written, or come across, implementations that significantly improve on access time or memory overhead? or at least, that can improve these things given some assumptions?
From looking at the JDK source I can't believe that it can't be made faster or leaner.
I am aware of Commons Collections, but I don't believe it has any implementation whose goal is to be faster or leaner. Same for Google Collections.
Update: Should have noted that I do not need thread safety.
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HashMap, being a hashtable-based implementation, internally uses an array-based data structure to organize its elements according to the hash function. HashMap provides expected constant-time performance O(1) for most operations like add(), remove() and contains(). Therefore, it's significantly faster than a TreeMap.
Java TreeMapThe TreeMap class is efficient for traversing the keys in a sorted order. The keys can be sorted using the Comparable interface or the Comparator interface. SortedMap is a subinterface of Map, which guarantees that the entries in the map are sorted.
The Java Map interface, java. util. Map , represents a mapping between a key and a value. More specifically, a Java Map can store pairs of keys and values. Each key is linked to a specific value.
Normally these methods are pretty quick. There are a couple of things you should check: are your hash codes implemented? Are they sufficiently uniform? Otherwise you'll get rubbish performance.
http://trove4j.sourceforge.net/ <-- this is a bit quicker and saves some memory. I saved a few ms on 50,000 updates
Are you sure that you're using maps/sets correctly? i.e. not trying to iterate over all the values or something similar. Also, e.g. don't do a contains and then a remove. Just check the remove.
Also check if you're using Double vs double. I noticed a few ms performance improvements on ten's of thousands of checks.
Have you also set up the initial capacity correctly/appropriately?
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