import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Set;
import java.util.HashSet;
public class HashCodeForString{
    public static void main(String[] args) {
        // Create a hash set
        Set<String> set = new HashSet<>();



        // Add strings to the set
      //  set.add("az");
       // set.add("Java");
     //   set.add("Programming");
        set.add("Justin Clark");


        //ArrayList<String> myArrayList = setToList(set);

        // Display the hash code for each element in the array list
        for (String str : set) {
            System.out.println("The hash code for \"" + str + "\" = "+ hashCodeForString(str));
        }
    }

        // Return a hash code for a string
        public static int hashCodeForString(String s) {
            int myhash = 0;

            //Algorithm:  s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
            for (int i = 0; i < s.length(); i++){
            	int n = s.length() - (i + 1);
            	BigInteger exp = BigInteger.valueOf(31);
            	exp = exp.pow(n);


            	myhash += (exp.multiply(BigInteger.valueOf(s.charAt(i))).intValue());
            }
            int realHash = s.hashCode();
            return myhash;
        }

        public static int testHashCode(String s) {
        	//Modified hash version found online.
        	//Supposedly the version java uses internally for String objects
        	//Found at http://java-bytes.blogspot.com/2009/10/hashcode-of-string-in-java.html
        	int h = 0;

        	for (int i = 0; i < s.length(); i++) {
        		h = 31*h + s.charAt(i);
        	}

        	return h;
        }

        // Return an ArrayList from a set
        public static <E> ArrayList<E> setToList(Set<E> s) {
            ArrayList<E> mylist = new ArrayList<E>();
                for(E i : s)
                    mylist.add((E) i);
                return mylist;
            }

        }