TableView on javafx showing empty rows

Question

I wanted to create a method that would return me a table in BorderPane ,but I got the empty table and the label of it shown on the GUI. Here's the code:

@Override
public void start(Stage stage) throws Exception {
    BorderPane border = new BorderPane();
    VBox cbox = addCbox(); //center box
    border.setCenter(cbox);
  
    Scene scene = new Scene(border, 600, 650);
    stage.setTitle("Test Project"); // Set the stage title
    stage.setScene(scene); // Place the scene in the stage
    stage.show(); // Display the stage
}

This is how I create the table data and the method by following the documentation:

private final TableView<Doctor> table = new TableView<>();
    private final ObservableList<Doctor> data = FXCollections.observableArrayList(
        new Doctor("196", "Daniel LW", "Cardiologists", "9-6", "MBBCh"),
        new Doctor("197", "James DN", "Anesthesiologists", "4-9", "LRCP"),
        new Doctor("199", "Chales AK", "Dermatologists", "6-12", "BSc")
    );

    public static void main(String[] args) {
        launch(args);
    }

    public VBox addCbox() {
        final Label label = new Label("Doctor List");
        label.setFont(new Font("Arial", 20));
        table.setEditable(true);
        
        TableColumn<Doctor, String> col1 = new TableColumn<Doctor, String>("ID");
        col1.setMinWidth(30);
        col1.setMaxWidth(60);
        col1.setCellValueFactory(new PropertyValueFactory<>("id"));
        
        TableColumn<Doctor, String> col2 = new TableColumn<Doctor, String>("NAME");
        col2.setMinWidth(100);
        col2.setCellValueFactory(new PropertyValueFactory<>("name"));

        table.setItems(data);
        table.getColumns().addAll(col1,col2);
        // the above line prompt me warning message, but although I use:
        // table.getColumns().add(col1); table.getColumns().add(col2);
        // the rows of data still not visible
        // I only get the empty clickable rows

        final VBox cbox = new VBox();
        cbox.setPadding(new Insets(10,20,10,10));
        cbox.getChildren().addAll(label,table);
        
        return cbox;
    }

And this is the shortened version of the class I created. There are setters and getters.

public static class Doctor {
    private SimpleStringProperty id, name, specialist, workTime, qualification;
        
    public Doctor(String id, String name, String specialist, String workTime, String qualification) {
        this.id = new SimpleStringProperty(id);
        this.name = new SimpleStringProperty(name);
        this.specialist = new SimpleStringProperty(specialist);
        this.workTime = new SimpleStringProperty(workTime);
        this.qualification = new SimpleStringProperty(qualification);
    }
}