Java RandomGenerator no reponse to be repeated twice in a row

I need to output random number that relate to a repose. So to pick one i need to generate a random number with no number repeated twice in a row. I know you have to store the previous value but do not know where to start. Here my code.

private String pickDefaultResponse()
{
    // Pick a random number for the index in the default response list.
    // The number will be between 0 (inclusive) and the size of the list (exclusive).
    int prevIndex;
    int newIndex;
    int index = randomGenerator.nextInt(defaultResponses.size());

    return defaultResponses.get(index);                
 }