Java Tip 139: Ask the right questions in your survey application

// Implement this interface to display question and accept answer
public interface QuestionInteraction
{
    // Use of double dispatch when the implementation of this interface
    // sets the answer (second dispatch)
    public void answer(Question q);
}

// Interface to provide the source of all actions.  The actions
// are already wired together (decision tree).
public interface ActionSource
{
    /** Get the starting action. */
    public Action getStartingAction();
    /** Get the action given its ID. */
    public Action getAction(String id);
}

public class ActionFlow
{
    //......
    /** Set the source of the actions. */
    public void setSource(ActionSource src) {
        actionSource_ = src;
        if (src != null)
            currentAction_ = src.getStartingAction();
    }
    public boolean isComplete() { return complete_; }
    public Action getCurrentAction() { return currentAction_; }
    /** Move forward one step in the flow, if possible. */
    public void moveForward()
    {
        //......
        Action next = getNextAction();
        if (next != null)
        {
            next.setPreviousAction(currentAction_);
            currentAction_ = next; //move forward
        }
        //......
    }
    /** Move backward one step in the flow, if possible.
     *  Otherwise, stay at current step. */
    public void moveBackward()
    {
        //......
        Action prev = currentAction_.getPreviousAction();
        if (prev != null) {
            currentAction_.setPreviousAction(null);
            currentAction_ = prev; //move backward
            complete_ = false;
        }
    }
    /** Answer the current question (current step is assumed to
     *  be a Question). */
    public void perform()
    {
        currentAction_.perform();
        moveForward();
    }
}

   try {
      System.out.println("Processing file " + dataFile);
      final DocumentBuilder db = getDocBuilder(); // Get an XML document builder
      final Document doc = db.parse(new FileInputStream(dataFile));
       ActionLoader loader = new ActionLoader(doc);
       ActionFlow flow = new ActionFlow(loader);
      while (!flow.isComplete())
         flow.perform();
   }
   catch (...) {
   }

 <act:ActionList version="1.0" xmlns:act="http://www.good_thang.net/xmlns/ActionList">
<act:Action id="1" type="Question">
   <act:Content value="What type of vehicle did you purchase?" />
   <act:Explanation value="Pick your choice" />
   <act:AnswerList>
      <act:Answer value="Car" consequence="2" />
      <act:Answer value="Truck" consequence="3" />
      <act:Answer value="SUV" consequence="4" /> 
   </act:AnswerList>
</act:Action>
<act:Action id="2" type="Question">
   <act:Content value="What type of car?" />
   <act:AnswerList>
   <act:Answer value="Sport Coupe" /> 
   <act:Answer value="Sedan" />
   </act:AnswerList>
</act:Action>
<act:Action id="3" type="Question">
   <act:Content value="What type of truck?" /> 
   <act:AnswerList>
      <act:Answer value="Pickup" /> 
      <act:Answer value="4x4" /> 
   </act:AnswerList>
</act:Action>
<act:Action id="4" type="Question">
   <act:Content value="Which brand of SUV?" /> 
   <act:AnswerList>
      <act:Answer value="Fore Runner" /> 
      <act:Answer value="Passport" /> 
      <act:Answer value="Path Finder" /> 
   </act:AnswerList>
</act:Action>
</act:ActionList>