JavaFX Hibernate 返回 Null 指针异常

Question

I'm a newbie here in Stackoverflow and this is my first time putting my questions here since I always research anything about my programming basics.
The problem I am facing now is the Null Pointer Exception. I am working in JavaFX Hibernate for the first time and it seems Null Pointer Exception is absolutely present with my basic practice:(
so here is my problem. . I will provide the codes. . hope you will get it:(

//Model(Pojo) Code

@Entity
@Table(name = "person")
public class Person implements Serializable {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id", nullable = false)
private Integer id;
@Column(name = "first_name", nullable = false)
private String firstName;
@Column(name = "last_name", nullable = false)
private String lastName; //including the setters and getters here}

//Repository Code

@Override
public List<Person> getPerson() {
    session = sessionFactory.openSession();
    try {
        String hql = "From Person";
        //System.out.println(hql);
        return session.createQuery(hql).list();
        
    } finally {
        session.close();
    }
}

//Service Code

public interface PersonService {
List<Person> getPerson();}

Controller Code (where the NPE Persist)

 @FXML
private TableView<Person> table;
@FXML
private TableColumn<Person, Integer> id;
@FXML
private TableColumn<Person, String> firstname;
@FXML
private TableColumn<Person, String> lastname;
private final ObservableList<Person> person = FXCollections.observableArrayList();

void getAllData() {
    List<Person> personList = personService.getPerson();
    person.addAll(personList);
    id.setCellValueFactory(new PropertyValueFactory<>("id")); //returns NPE here
    firstname.setCellValueFactory(new PropertyValueFactory<>("firstName"));
    lastname.setCellValueFactory(new PropertyValueFactory<>("lastName"));
    table.setItems(person);
}

//FXML Code in package 'forms' (forms/FormX.fxml)

<AnchorPane id="AnchorPane" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8.0.171" xmlns:fx="http://javafx.com/fxml/1" fx:controller="controller.Controller"> <children> <AnchorPane prefHeight="400.0" prefWidth="606.0"> <children> <TextField fx:id="fname" layoutX="14.0" layoutY="61.0" prefHeight="25.0" prefWidth="200.0" promptText="Firstname" /> <TextField fx:id="lname" layoutX="14.0" layoutY="102.0" prefHeight="25.0" prefWidth="200.0" promptText="Lastname" /> <Button fx:id="btn_save" layoutX="14.0" layoutY="141.0" mnemonicParsing="false" onAction="#SaveData" text="SAVE " /> <Button layoutX="154.0" layoutY="141.0" mnemonicParsing="false" text="CANCEL" /> <TableView fx:id="table" layoutX="258.0" layoutY="27.0" prefHeight="352.0" prefWidth="324.0"> <columns> <TableColumn fx:id="id" prefWidth="75.0" text="id" /> <TableColumn fx:id="firstname" prefWidth="75.0" text="firstname" /> <TableColumn fx:id="lastname" prefWidth="75.0" text="lastname" /> </columns> </TableView> </children> </AnchorPane> </children> </AnchorPane>

Error Returns: j ava.lang.NullPointerException: Cannot invoke "javafx.scene.control.TableColumn.setCellValueFactory(javafx.util.Callback)" because "this.id" is null


I created a Persistence Unit (persistence.xml) the connection is good and I can connect.

So this is my problem, the "id" always returning NPE and I'm pointing it on the Pojo. I don't know how to get rid of this as I research about this for how many links:( I do hope I can get an answer in this query. thanks!

Answer 1

So Basically I solved my problem for an hour. lol
so I put the getAllData(); method in my Controller in the

void intialize(URL url, ResourceBundle rb){//I put it here}

it sounds weird but I realized it after a lot of research without finding an answer lol. so I tried to relax and stare at my code then the idea miraculously appear. LOL. I tried to figure it out now what is the problem with my previous logic. the last one I did was putting the getAllData in the main Class or the Launcher after the stage.show(); and the NPE persist here. if anyone can explain me why cause I can't figure it out. please share your idea to me. thanks