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;}