Collections Sort to sort both ArrayLists the same

Question

My program has to use the Collections sort method to sort the ArrayList of Strings lexicographically but each String has a corresponding integer value stored in a separate ArrayList. I want to sort them both the same so the integer values stay with the correct Strings. And if you know a better way to store both values I'm all ears.

public class a5p1b {
    public static void main(String[] args) {

        Scanner input = new Scanner(System.in).useDelimiter("[^a-zA-z]+");
        // ArrayLists to store the Strings and the frequencies
        ArrayList<String> lst = new ArrayList<String>();
        ArrayList<Integer> intLst = new ArrayList<Integer>();

        //loops through as long as there is user input
        while (input.hasNext()) {
            String str = input.next().toLowerCase();
            // if the list already has the string it doesn't add it and it
            // ups the count by 1
            if (lst.contains(str)) {
                int index = lst.indexOf(str);
                intLst.set(index, intLst.get(index) + 1);
            } else {
                // if the word hasnt been found yet it adds it to the list
                lst.add(str);
                intLst.add(1);
            }
        }
    }    
}

Answer 1

You are getting your abstractions wrong. If that string and that number belong together, then do not keep them in two distinct lists.

Instead create a class (or maybe use one of the existing Pair classes) that holds those two values. You can then provide an equals method for that class; plus a specific comparator, that only compares the string elements.

Finally, you put objects of that class into a single list; and then you sort that list.

The whole idea of good OO programming is to create helpful abstractions!

For the record: as dnault suggests, if there is really no "tight" coupling between strings and numbers you could also use a TreeMap (to be used as TreeMap<String, Integer>) to take care of sorting strings that have a number with them.