How can I use a variable that I was passing from one controller to another in my SQL query javafx

Question

I have this variable that I passed from one controller to another it's the username and the password and then I wanted to use them to make a SQL query but it's not working.

I am really really new with javafx and I have no idea how to correct this and I need it now for a project.

The variables t and tot contain the username and password that I passed from the first controller.

private String[] T = new String[2];
    public void myFunctione(String text){
        label.setText(text);
    }
    public void yFunctione(String text){
        labele.setText(text);
    }
    
    @Override
    public void initialize(URL location, ResourceBundle resources) {
        System.out.print(label.getText());
        System.out.print(labele.getText());
        
        //(R) sql query in which I used label and labele 

This is the code of the controller that displays the students table. What I did now is that I put the two variables "username" and "password" in the labels "label" and "labele" and I don't know why I can't insert the value of these labels in the SQL query.

    public void viewStudents(ActionEvent e) throws IOException{
        
        Stage primaryStage=new Stage();
        FXMLLoader Loader= new FXMLLoader(getClass().getResource("ViewStudents.fxml"));
        Parent root = Loader.load();
        ViewStudents con = Loader.getController();
        con.myFunctione(label1.getText());
        con.yFunctione(label2.getText());
        Scene scene = new Scene(root,808,400);
        scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
        
        primaryStage.setScene(scene);
        primaryStage.show();
    }

Answer 1

The following is an mre of setting values of 2 labels to another controller:

ViewStudents.fxml has only a label. The label should show the two strings passed to the controller:

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.HBox?>


<HBox xmlns="http://javafx.com/javafx/10.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="fx_tests.ViewStudents">
   <children>
      <Label fx:id="sqlText" prefHeight="17.0" prefWidth="224.0" text="Press button to show sql text" HBox.hgrow="ALWAYS" />
   </children>
</HBox>

Its controller that can receive two Strings and set them to the label:

import javafx.fxml.FXML;
import javafx.scene.control.Label;

public class ViewStudents {

@FXML private Label sqlText;

    void setStudentDetails(String name, String password){
        sqlText.setText("name: "+ name + " password: " + password);
    }
}

Simple application to test it:

import java.io.IOException;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.geometry.Insets;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.scene.layout.VBox;
import javafx.scene.text.Text;
import javafx.stage.Stage;

public class FxmlTest extends Application {

    private Button updateStudentsView;
    private Label name, password;
    private ViewStudents con;

    @Override
    public void start(Stage primaryStage) {

        Pane viewStudents = null;
        try {
              FXMLLoader Loader= new FXMLLoader(getClass().getResource("ViewStudents.fxml"));
              viewStudents = Loader.load();
              con = Loader.getController();
        } catch (IOException ex) {
            ex.printStackTrace();
        }

        name = new Label("sarah");
        password = new Label("89");
        updateStudentsView = new Button("Update Students View");
        updateStudentsView.setOnAction(e->viewStudents());
        HBox studentsDetails = new HBox(20,new Text("Strudent details: "), name,password, updateStudentsView);

        Pane root = new VBox(20, studentsDetails, viewStudents);
        VBox.setMargin(studentsDetails, new Insets(20));
        VBox.setMargin(viewStudents, new Insets(20));

        Scene scene = new Scene(root, 400, 300);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private void viewStudents() {
        con.setStudentDetails(name.getText(), password.getText());
        updateStudentsView.setDisable(true);
    }

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

After you have set the content of the two labels you can use it to prepare an sql statement, for example:

   void setStudentDetails(String name, String password){
      try {

             String sql= "SELECT s.id , s.nom , s.prenom , s.email , s.filiere , s.date  FROM `students` as s JOIN `profs` as p ON p.id=s.idfk WHERE p.username=? AND p.password=?"; 
             Connection con=AdminsDB.getConnection();
             PreparedStatement preparedStatement=(PreparedStatement)con.prepareStatement(sql);
             preparedStatement.setString(1,name);
             preparedStatement.setString(2,password);

             ResultSet rs=preparedStatement.executeQuery();

             while(rs.next()){
                 data.add(new Students(rs.getInt(1),rs.getString(2),rs.getString(3),rs.getString(4),rs.getString(5),rs.getString(6)));
             }
             con.close();
        }catch (SQLException e) {
            e.printStackTrace();
        }
    }