java - Null pointer exception in One To Many Mapping example -

employee class :

public class employee {

private int employee_id;  private int faculty_no;  private int enrolment_no;  private string firstname;  private string lastname;  private date birth_date;  private string cellphone;  private department dep;  //getters , setters 

}

department class :

public class department {

private long department_id;  private string department_name;  private string department_location;  private string department_rank;  set<employee> employee_list;      // getters , setters 

}

impl class :

public class onetomanyimpl {

public static void main(string[] args) {      sessionfactory sessionfactory = hibernateutility.getsessionfactory();      session session = sessionfactory.opensession();      session.begintransaction();      department department = new department();      department.setdepartment_name("mechanical dept.");      department.setdepartment_rank("a class");      department.setdepartment_location("university");     session.save(department);       employee emp = new employee();     emp.setenrolment_no(2007255);     emp.setenrolment_no(3794);     emp.setfirstname("firstname");     emp.setlastname("gernaline");     emp.setbirth_date(new date());     emp.setcellphone("011899954");     emp.setdep(department);      department.getemployee_list().add(emp);          session.save(emp);          session.gettransaction().commit();          session.close();  } 

}

even after adding whole set, getting null pointer exception @ line : department.getemployee_list().add(emp); getting wrong?

in department class, have not initialized set , have not done before persisting well.

so either set<employee> employee_list = new hashset<employee>();in department class.

or below before persisting department object

department.setemployee_list(new hashset<>()); department.getemployee_list().add(emp);