这里的第三行是什么问题

Question

package pakage;public class DynamicBindingDemo { public static void main(String args[]) { m(new GraduateStudent()); m(new Student()); m(new Person()); m(new Object()); } public static void m(Object x) {//Object类型可以用任何类型访问它 System.out.println(x.toString()); } class GraduateStudent extends Student{ }class Student extends Person{ public String toString() { return "Student"; }}class Person extends Object{ public String toString() { return "Person"; }}}

Answer 1

？什么意思