Analyze the following code: public class A { public static void main(String[] args) { A a = new AO; a(1); System.out.println("A1:" + a); } static void a(int n) { n++ } } The code has a compile error because variable "a" cannot be printed. The code prints "A1:1". The code prints "A1:" followed by the hexadecimal reference value for variable "a". The code prints "A1:null