Program to count the number of unique words in a file using HashMap

import java.io.File;
import java.io.FileNotFoundException;
import java.util.*; 
public class CountUniqueWords {

    public static void main(String args[]) throws FileNotFoundException { 

        File f = new File("C:/547647/word.txt");
        ArrayList arr=new ArrayList();
        HashMap<String, Integer> listOfWords = new HashMap<String, Integer>(); 
        Scanner in = new Scanner(f);
        int i=0;
        while(in.hasNext())
        {
        String s=in.next();
        //System.out.println(s);
        arr.add(s);
        }
        Iterator itr=arr.iterator();
        while(itr.hasNext())
        {i++;

            listOfWords.put((String) itr.next(), i);
            //System.out.println(listOfWords);
        }

        Set<Object> uniqueValues = new HashSet<Object>(listOfWords.values()); 

        System.out.println("The number of unique words: "+uniqueValues.size());



}
}