Try-Catch Problem

I am trying to do a try catch concerning the entering of letters.  When i enter a letter I display the message that says, you must enter a number, however my problem is that the user is not returned to the dialog box to re-enter the number.  It skips to the next dialog box.  I believe that I may have my try-catch in the wrong position or am missing one line.  Any assitance is appreciated.

BJ

  do {                
             
            valid=false;
                assignment1 = JOptionPane.showInputDialog(null, "Please Enter The Assigment Grade For The Student" );                        
                             
            try {
               
           
                assignment1S[i] = Double.parseDouble( assignment1 );
               
            } catch(NumberFormatException e){    
                     
             JOptionPane.showMessageDialog( null, "You did not enter a number, please try again.");              
               
             valid=true;
             
            }
                                       
               if ((assignment1S[i] < 0) || (assignment1S[i] > 100))
                   
                   JOptionPane.showMessageDialog( null, "Please enter a number between 0 and 100.");                  
                   
               
         
            } while ((assignment1S[i] < 0) || (assignment1S[i] > 100));