Question

I am new to java.
I want to sort a concurrent hash map by value. I found a way of doing it here –
sort concurrent map entries by value

Is there a simpler way of doing it? Can someone please explain it with an example ?

Thanks.

Answer 1

Another solution would be to switch to using the ConcurrentSkipListMap which was added in Java 6. To quote from the Javadocs:

This class implements a concurrent variant of SkipLists providing expected average log(n) time cost for the containsKey, get, put and remove operations and their variants. Insertion, removal, update, and access operations safely execute concurrently by multiple threads. Iterators are weakly consistent, returning elements reflecting the state of the map at some point at or since the creation of the iterator. They do not throw ConcurrentModificationException, and may proceed concurrently with other operations. Ascending key ordered views and their iterators are faster than descending ones.

SkipLists are probabilistic replacements for balanced trees. They have the same O as trees but usually their implementation is markedly simpler. If most of your operations are hash-table lookups (O(1) by definition) then you will see a performance different for decent table sizes, but if you require sorting often, this may be a better solution.

I just wish Java provided a non-concurrent version of this great data structure.