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 firstName, String surname, String address, String phoneNumber) {
this.firstName = firstName;
this.surname = surname;
this.address = address;
this.phoneNumber = phoneNumber;
this.employeeNumber = employeeIdCounter++;
}