PBO-C 5 : Responder()

import java.util.*;

public class Responder
{
    private Random randomGenerator;
    private ArrayList<String> responses;
    private HashMap<String, String> responseMap;

    public Responder()
    {
        randomGenerator = new Random();
        responses = new ArrayList<String>();
        responseMap = new HashMap<String, String>();
        fillResponses();
        fillResponseMap();
    }

    public String generateResponse(HashSet<String> words)
    {
        for(String word:words)
        {
            String response=responseMap.get(word);
            if(response!=null)
            {
                return response;
            }
        }

        int index = randomGenerator.nextInt(responses.size());
        return responses.get(index);
    }

    private void fillResponses()
    {
        responses.add("Sorry, i dont understand you");
        responses.add("Please try another word");
    }

    private void fillResponseMap()
    {
        responseMap.put("problem", "Can you describe more about the problem?");
        responseMap.put("bug", "What kind of bug?");
        responseMap.put("error", "What kind of error?");
        responseMap.put("stop", "You can restart the program");
        responseMap.put("thanks", "You're Welcome");
    }
}