Build regular expressions for the following examples:
        
        
          - 
            The string "Dragon".
- 
            The strings "Alice" or "Bob".
- 
            Any non-empty string of digits.
          
- 
            Any string of digits of length exactly 5 characters.
          
- 
            Any non-empty string of digits of length less than or
            equal to 3 characters.
          
- 
            Simple URLs of the form
            "http://fpl.cs.depaul.edu".
- 
            The tokens of your favourite programming language (as long
            as it is Java).
          


