由于您的超类 Person 没有默认构造函数，因此在您的子类 (Student和 Staff)，则必须调用超类构造函数作为第一条语句.

Since your super class Person doesn't have a default constructor, in your sub classes (Student and Staff), you must call the super class constructor as the first statement.

你应该像这样定义你的子类构造函数:

You should define your sub class constructors like this:

Student() {
    super("a_string_value", an_int_value);// You have to pass String and int values to super class
}

Staff() {
    super("a_string_value", an_int_value); // You have to pass String and int values to super class
}