Why am I receiving negative values for my hash function?

Question

I have this hash function that calculates a key based on the product of a words ASCII values. It was working fine when I tested it with small words, but then I tried words from a whole text file and some of them get negative values while others are positive. I understand that this is overflow, but how would I fix it?

EDIT: Ok, so people are saying that negative hash values are valid. My problem is that I implemented the hash table using an array and I am getting an index out of bounds error due to the negative numbers. What would be the best way to fix this?

public int asciiProduct(String word) {
  // sets the calculated value of the word to 0
  int wordProductValue = 1;

  // for every letter in the word, it gets the ascii value of it
  // and multiplies it to the wordProductValue
  for (int i = 0; i < word.length(); i++) {
    wordProductValue = wordProductValue * (int) word.charAt(i);
  }

  // the key of the word calculated by this function will be set 
  // to the modulus of the wordProductValue with the size of the array
  int arrayIndex = wordProductValue % (hashArraySize-1);
  return arrayIndex;
}

Answer 1

You can just take the absolute value of the result of your integer multiplication - which will overflow to a negative number when the integer value gets too big.

wordProductValue = Math.abs(wordProductValue * (int) word.charAt(i));

However, your hash function using modulo via the % operator should still work even with a negative number.

Answer 2

A negative hash code is perfectly valid. There is nothing wrong with it. No need to "fix". But may I ask why are you doing this?

word.hashCode() should give you a much better hash value, than this ...