/**
 * A demo of a hash function for Strings.
 */
public class StringHash {

    /**
     * This code computes the built-in hash function of the String
     * class (present as the hashCode method of the String class).
     * Computes a weighted sum of the individual letters of
     * the string (designed to evenly balance hash values among
     * different strings without biasing towards, e.g.,
     * particular or smaller values).
     */
    public static int stringHashCode(String s) {
        char[] chars = s.toCharArray();
        int hash = 0;
        for (int i = 0; i < chars.length; i++) {
            hash = 31 * hash + chars[i];
        }
        return hash;
    }

    /**
     * Given a string, print the hash value using the stringHashCode utility method
     * and the built-in hashCode method of the String class.
     */
    private static void test(String s) {
        System.out.println("\"" + s + "\" hash code is " + stringHashCode(s));
        System.out.println("\"" + s + "\" hash code (built-in) is " + s.hashCode());
    }

    /**
     * Compute some String hash values.
     */
    public static void main(String[] args) {
        test("Bowdoin");
        test("College");
        test("the");
        test("");
        test("computer science is the best");
    }

}