Java Projects - Second Edition

Hash functions

A hash is a mathematical function that assigns a number to an element. Sounds terrible, doesn't it? Say you work as a university admin and you have to tell whether Wilkinson is a student in your class. You can store the names on small papers in envelopes, one for each starting letter. Instead of searching through the 10,000 students, you can look at the papers in the envelope titled W. This very simple hash function assigns the first letter of the name to the name (or the ordinal number of the letter, as we said that a hash function results a number). This is not really a good hash function because it puts only a few elements, if any, into the envelope denoted X and many into A, for example.

A good hash function returns each ...