Adding Actions to the Automaton

Once you have an automaton that recognizes the data, adding statements that perform the right actions takes a few more steps. Look at this method which implements the date automaton. It returns a MyDate object if the argument is valid, or null if not. But it is not quite complete. It still needs a few more steps.

  MyDate convert( String str )
  {

    int  reject= 10;       // rejection state
    int  state = 1;        // the current state
    char current;          // the current character
    int  index = 0 ;       // index of the current character

    while ( index < str.length()  && state != reject  )
    {
      current = str.charAt( index++ ) ;

      if      ( state==1 && current >=  '0' && current <= '9')
      {
        state = 2;
      }
      else if ( state==2 && current=='/' )
      {
        state = 4;
      }
      else if ( state==2 && current >=  '0' && current <= '9' )
      {
        state = 3;
      }
      else if ( state==3 && current=='/' )
      {
        state = 4;
      }
      else if ( state==4 && current >=  '0' && current <= '9' )
      {
        state = 5;
      }
      else if ( state==5 && current=='/' )
      {
        state = 7;
      }
      else if ( state==5 && current >=  '0' && current <= '9' )
      {
        state = 6;
      }
      else if ( state==6 && current=='/' )
      {
        state = 7;
      }
      else if ( state==7 && current >=  '0' && current <= '9' )
      {
        state = 8;
      }
      else if ( state==8 && current >=  '0' && current <= '9' )
      {
        state = 9;
      }
      else
        state = reject ;
    }

    if ( index == str.length()  && state == 9  )
      return new MyDate( day, month, year )  ;
    else
      return null ;
  }

Your goal is to change the automaton as little as possible. The automaton has solved the "recognize" part of the problem. For the most part, you should just add statements to the automaton to finish the "compute" part of the problem. A few changes have been made to the original automaton: the return type MyDate is constructed in the last if-else of the method.