ConcurerntSkipListMap

Java 6 adds a further weapon to the collections armoury in the form of the ConcurrentSkipListMap. In terms of its general functionality, this class is a kind of cross between a ConcurrentHashMap and a TreeMap. In other words:

like ConcurrentHashMap, it allows modifications without locking the entire map;
like TreeMap, it maintains the keys permanently sorted, thus providing an efficient means of retrieving a submap containing mappings of all the keys within a particular range (in terms of the API, this means it implements SortedMap).

However, compared to ConcurrentHashMap, ConcurrentSkipListMap has some different performance characteristics:

it provides more scalable concurrency even over ConcurrentHashMap;
this concurrency is paid for with non-constant access times.

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