如何创建一个生成与此正则表达式匹配的字符串的方法？

Question

I have these regular expression:

M := (M)
M := n

These expressions can generate strings such as: ((((n)))), n, (n), etc.

I have to create a method that can check if a string is part of the grammar, it doesn't necessarily has to be a code, it is more like the step before you start coding

class Sintax {
    Lexic l = new Lexic();
    int p = 0;
    void M(){
       if(lexicalSImbol == 'n')
       {
           if(p != 0)
              checkParentesis();
           else
              checkEndOfString();
       }
       else if(lexicalSimbol == '(')
       {
           p++;
           M();
       }
       else
          error();
    }

    void checkParentesis(){
       int i = 1;
       while(i <= p)
       {
           if(l.nextSimbol() == ')')
              i++;
           else
              error();
       }
    }
}

But I am not sure if the method is able to deliver all of the strings that the grammar can generate, or if I can change it in some way to make it more efficient.

Answer 1

checkParentesis has to end with checkEndOfString(); for an erroneous input "(n))" . So the code can be reduced:

void M(){
   if(lexicalSImbol == 'n')
   {
       //checkParentesis();
       while (p > 0 && l.nextSimbol() == ')')
           --p;
       checkEndOfString();
   }
   else if(lexicalSimbol == '(')
   {
       p++;
       M();
   }
   else
      error();
}