operator int*() vs int* operator ()()

?

class AA{

public:

    operator int*()          {return NULL;}

    int* operator ()()       {  return NULL;}

    int* operator ()(int k)  {return NULL;} };

int main(){ AA a;

    int *p;

    p = a;

    p = a();

    p = a(2);

    return 0;}