Login Form Java MySQL fails in intellij

you did not intitialize the PreparedStatement variable , just declared with null value PreparedStatement pst = null;

so when the statement rs = pst.executeQuery(query); executing then throwing an error. and in your catch block you have written only System.out.println("Wrong UserName Or Password");. so you are getting error "Wrong UserName Or Password"

but actual error is you did not initialize the PreparedStatement pst variable before executing the query.

so initialize the pst variable to resolve your problem

if you want to know how to use prepared statement then you can see from here with example

and i have resolved the all issues of your code, so simply you can copy and paste the below code , hope it will be helpful for you

package sample;

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.*;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.scene.text.Font;
import javafx.stage.Stage;


import java.sql.*;
import java.util.logging.Level;
import java.util.logging.Logger;

public class DataBaseProject1 extends Application {

    Connection conn;
    PreparedStatement pst = null;
    ResultSet rs = null;

    @Override
    public void start(Stage primaryStage) throws Exception
    {
        //GUIS a = new GUIS();
        //a.createConnection();
        //a.display();
        DataBaseProject1 d = new DataBaseProject1();
        d.createConnection();

        primaryStage.setTitle("Retrive Database Values Into CheckBox");

        //primaryStage.getIcons().add(new Image("file:user-icon.png"));
        BorderPane layout = new BorderPane();
        Scene newscene = new Scene(layout, 1200, 700, Color.rgb(0, 0, 0, 0));

        Group root = new Group();
        Scene scene = new Scene(root, 320, 200, Color.rgb(0, 0, 0, 0));
        scene.getStylesheets().add(getClass().getResource("Style.css").toExternalForm());

        Color foreground = Color.rgb(255, 255, 255, 0.9);

        //Rectangila Background
        Rectangle background = new Rectangle(320, 250);
        background.setX(0);
        background.setY(0);
        background.setArcHeight(15);
        background.setArcWidth(15);
        background.setFill(Color.rgb(0 ,0 , 0, 0.55));
        background.setStroke(foreground);
        background.setStrokeWidth(1.5);

        VBox vbox = new VBox(5);
        vbox.setPadding(new Insets(10,0,0,10));

        Label label = new Label("Label");
        //label.setTextFill(Color.WHITESMOKE);
        label.setFont(new Font("SanSerif", 20));

        TextField username = new TextField();
        username.setFont(Font.font("SanSerif", 20));
        username.setPromptText("Username");
        username.getStyleClass().add("field-background");

        PasswordField password =new PasswordField();
        password.setFont(Font.font("SanSerif", 20));
        password.setPromptText("Password");
        password.getStyleClass().add("field-background");

        Button btn = new Button("Login");
        btn.setFont(Font.font("SanSerif", 15));
        btn.setOnAction(e ->{
            try{
                String user = username.getText();
                String pass = password.getText();
                String query = "SELECT * FROM userdatabasetable Where UserName = " + "'" + user + "'" + " AND Password = " + "'" +pass + "'" + " ";
                d.pst=d.conn.prepareStatement(query);
                rs = d.pst.executeQuery(query);

                if(rs.next()){
                    label.setText("Login Successful");
                    primaryStage.setScene(newscene);
                    primaryStage.show();
                }else{
                    label.setText("Login Failed");
                }
                username.clear();
                password.clear();
                d.pst.close();
                rs.close();
            }catch(Exception e1){
                label.setText("SQL Error");
                System.out.println("Wrong UserName Or Password");
                //System.err.println(e1);
               // e1.printStackTrace();
            }
        });

        vbox.getChildren().addAll(label, username, password, btn);
        root.getChildren().addAll(background, vbox);

        primaryStage.setScene(scene);
        primaryStage.show();
    }

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

    Connection createConnection ()
    {
        try
        {
            //Class.forName("com.mysql.jdbc.Driver");
            Class.forName("com.mysql.cj.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/UserDataBase","yusof","1234");
            System.out.println("DataBase Connected Successfully");

            //con.close();
        }
        catch (ClassNotFoundException | SQLException ex)
        {
            Logger.getLogger(DataBaseProject1.class.getName()).log(Level.SEVERE, null, ex);
        }
        return null;
    }
}