constructor of the class will be all the data except the employee number, which will be a generated number (the first employee to be employee number 1, the second employee number 2 and so on). and so on)

public Employee(String name, double salary, int month, int day, int year) {
        this.name = name;
        this.salary = salary;
        GregorianCalendar calender = new GregorianCalendar(year, month - 1, day);
        hireDay = calender.getTime();
    }