PoornaChandra Raju posted this question Oct 2, 2001: I am using JavaCC utility to generate a parser. I have three tokens defined say TokenA: "A", TokenB: "B" and TokenC: "C". I have to write a statement in my grammar such that, the above said tokens can appear in the any of the following ways; 1) All the tokens are optional Example : ABC or AB or Ac or A or nothing 2)The tokens can appear in any order Example: ABC or CBA or ACB or ..... 3) A token can appear only once Example: AAB ---> is wrong, becaue "A" appears twice. I have solved this problem using Jav   More>>