Hashing

please anybody help me regarding the Hashing process , what is the concept behind the hashmap,hashtable and hashset can anybody help in neat explained manner.Point is how hashmap,hashtable and hashset rely on hashing

For fast lookups, objects are stored in so-called buckets. Each bucket contains objects with the exact same hash code.

If the value for a key is looked up, its hash code is calculated first. Then the bucket for that hash code is retrieved. This will decrease the number of objects to search through - instead of checking every single object in the map / set, only the objects in the one bucket will be checked. The better your hash code, the better objects are distributed among buckets, and the faster your map / set becomes.

That also shows the reason why the hash code for equal objects should be the same as well - otherwise, the object will not be found. It also shows another issue: you cannot modify objects stored in the map / set (keys for maps only) in such a way that the hash code will change, or it will never be found again.