Several approaches are possible. Here is a very simple one based on your
code which assumes that there is a fixed number of questions - the Vector is
built to have an element corresponding to each question, and is then filled
with null values [each indicating an unanswered question].

As you add responses for questions a check is made to see if:

* The question number is valid
* The validated question has been answered or not

This should provide a reasonable starting point for your own solution.

I hope this helps.

Anthony Borla

// ------------------------------

// Test Code
...
       TestQuestions t = new TestQuestions(3);
       t.addResponses(new int[]{1,2,3}, 1);
       t.addResponses(new int[]{1,2,3}, 5);
       t.addResponses(new int[]{1,2,3}, 1);
...

// Code Proper
class TestQuestions
{
   private Vector q;

   public TestQuestions(int questions)
   {
       q = new Vector(questions);
       for (int i = 0; i < questions; i++)
           q.add(null);
   }

   public void addResponses(int[] responses, int questionNumber)
   {
       // Test for validity of questionNumber
       if (q.size() <= questionNumber)
       {
           // Not a valid question number ...
           System.err.println("Invalid question number ...");
       }
       // Check for existing responses for question
       else if (q.elementAt(questionNumber) == null)
       {
           // Currently unoccupied, so add responses
           q.add(questionNumber, responses);
       }
       else
       {
           // Question already answered
           System.err.println("Question already answered ...");
       }
   }
}