Java-将值从一类传递到另一类

Question

I am trying to pass a Strings from one class to another so I can initialize the labels according to the usernames.

Here's is my code:

    while (rs.next()) {
                    uID = rs.getString("ID");
                    uLoginName = rs.getString("user_login");
                    uNiceName = rs.getString("user_nicename");
                    password = rs.getString("user_pass");

                    if (uLoginName.equals(username) && password.equals(enteredPass)) {

                        ***//Values That I am Trying to pass***

                        TutorControlPanelController  panel  = new TutorControlPanelController();
                        panel.setUserLoginName(uLoginName);
                        try {

                            Parent root = FXMLLoader.load(getClass().getResource("SomePath"));
                            Scene scene = new Scene(root);
                            String css = this.getClass().getResource("Style.css").toExternalForm();
                            scene.getStylesheets().add(css);
                            Stage stage = new Stage();
                            stage.setTitle("Tutor Control Panel");
                            stage.setScene(scene);

                            stage.show();

                        } catch (IOException ex) {
                            Logger.getLogger(LoginController.class.getName()).log(Level.SEVERE, null, ex);
                        }
                    } else {
                        System.out.println("user not found");

                    }

                }

            } catch (SQLException ex) {
                Logger.getLogger(LoginController.class.getName()).log(Level.SEVERE, null, ex);
            }

in other Class , I am doing UPDATED

      public class SomeClass implements Initializable {

    @FXML
    private GridPane gridView;
    @FXML
    private Button recordButton;
    @FXML
    private Button stopButton;
    @FXML
    private MenuButton settingsButton;
    @FXML
    private MenuItem qualitySettings;
    @FXML
    private MenuItem videoSettings;
    @FXML
    private Button lessoncategory;
    @FXML
    private MenuButton serverUpload;
    @FXML
    private MenuItem startUpload;
    @FXML
    private MenuItem stopUpload;
    @FXML
    private Button timer;
    @FXML
    private Label timerHours;
    @FXML
    private Label timerMinutes;
    @FXML
    private Label timerSeconds;
    @FXML
    private Button logOut;
    @FXML
    private Label uNameLabel;

    private String uID;
    private String username;
    private String userLoginName;
    private String userNiceName;

    public TutorControlPanelController(String uID, String username, String userNiceName) {
        this.uID = uID;
        this.username = username;
        this.userNiceName = userNiceName;

    }

    /**
     * Initializes the controller class.
     */
    public TutorControlPanelController() {

    }

    public String getuID() {
        return uID;
    }

    public void setuID(String uID) {
        this.uID = uID;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getUserNiceName() {
        return userNiceName;
    }

    public void setUserNiceName(String userNiceName) {
        this.userNiceName = userNiceName;
    }

    public String getUserLoginName() {
        return userLoginName;
    }

    public void setUserLoginName(String userLoginName) {
        this.userLoginName = userLoginName;
    }

    @Override
    public void initialize(URL url, ResourceBundle rb) {

        assert uNameLabel != null : "fx:id=\"someID\" was not injected: check your FXML file 'somePath'.";

        setlabels();


    }

    public void setlabels() {
       uNameLabel.setText(getUserLoginName());

       // and just to check also printing the value

        System.out.println(getUserLoginName());
    }

All I am getting is null I am finding it hard to figure out what exactly is going on.

Answer 1

I dont see where do you call your first class in your second one. You must call the first one as an attribute to the seconde one for exemple, then you'll be able to get the userLoginName.

This is what you can do in your second class :

FirstClass myFirstClass = new FirstClass();
uNameLabel.setText(myFirstClass.getUserLoginName());

Answer 2

At the moment, the class TutorControlPanelController has a default constructor and a parameterized constructor. When the default constructor is invoked, the String instance variables are all initialized to null. They may be set by calling the various methods, but there is no guarantee they will be.

The better approach would be to remove the default constructor (delete this code):

public TutorControlPanelController() {

}

And in the code snippet with the rs.next(), change the call to use the parameterized constructor:

if (uLoginName.equals(username) && password.equals(enteredPass)) {
  TutorControlPanelController  panel  = new TutorControlPanelController(uId, uLoginName, uNiceName);

  try {
   ...

This approach would ensure that most of the instance variables were initialized.

However , as there is insufficient code here, I do not know if there is a framework requirement for the default constructor. If so, then initialize the String instance variables to have an empty String

private String uID = "";
private String username = "";
private String userLoginName = "";
private String userNiceName = "";

You will avoid NPEs in this case.