//QuestionNodes have a String data field as well as a reference to two other QuestionNodes.
public class QuestionNode{

   public String data;
   public QuestionNode yes;
   public QuestionNode no;
   
   //Constructs a new QuestionNode with no references so it is a leaf node.
   public QuestionNode(String data){
      this(data, null, null);
   }
   
   //Constructs a QuestionNode with references to the two specifified QuestionNodes.
   public QuestionNode(String data, QuestionNode yes, QuestionNode no){
      this.data = data;
      this.yes = yes;
      this.no = no;
   }
   
   //Checks it the QuestionNode is a leaf node.
   public boolean isAnswer(){
      return yes == null && no == null;
   }
}