Possible Duplicate:
How does Java hashmap work?
Can someone explain to me how HashSets in java work and why they are faster than using ArrayLists?
Possible Duplicate: How does Java hashmap work? Can someone explain to me how HashSets
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Possible Duplicate:
How does Java hashmap work?
Can someone explain to me how HashSets in java work and why they are faster than using ArrayLists?
First,
HashSet, unlikeArrayListis a Set: It cannot contain duplicates whileArrayListcan – so they are built for different purposes. It also does not guarantee ordering – again, unlike a list.Second – a
HashSetis built on the hash table data structure, that allowsO(1)seek time for an element.Note that many times, a
HashSetis slower then anArrayList– if you want to iterate on elements for example – usually doing it in anArrayListwill be faster then in aHashSet[because of bad cache performance of hash, among other reasons]