Computing Hash Codes

• A hash function computes an integer hash code from an object
• Choose a hash function so that different objects are likely to have different hash codes.
• Bad choice for hash function for a string
  • Adding the unicode values of the characters in the string

    int h = 0;
    for (int i = 0; i < s.length(); i++)
       h = h + s.charAt(i);

  • Because permutations ("eat" and "tea") would have the same hash code