Hashtable

• Hashing is designed to solve the problem of needing to efficiently find or store an item in a collection. It is a technique to narrow down the search space.
• Hashing means using some function or algorithm to map object data to some representative integer value.
• One basic approach. Calculate a hash for each key and store the hash value in an array index of the same value. Store the key, value pair in the same index positions in other arrays.
• However, this approach suffers from wasted space in the array - for those array indexes for which corresponding hash values are never generated.
• Another problem is collisions - a single hash value can represent many keys.
• To solve wasted space use : hashcode modulo arraysize.
• To solve collisions use linkedlists to store key->value pairs for each hash value.