how to retrive unique values from xmldatabase in blackberry

Question

I have xml database.In that database we stored 400 questions.i want read that questions randomly.not repeated same questions. i want read unique

        questions.

      This is quize type test questions.I am testing each time 50 questions .similarly 8 times i testing randomly.The questions read randomly .                

       what i am asking is that questions are not repeat in the test.  how to write code for this one in java.


      please help me.