package main;
import controller.ControllerClass;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;
import model.InitGui;
import view.*;
public class Main extends Application {
    public static void main(String[] args) {
    launch(args);
    }
    @Override
    public void start(Stage primaryStage) throws Exception {
           try {
                FXMLLoader loader = new FXMLLoader(getClass().getResource("/view/Design.fxml"));
                Parent root = loader.load();
                Scene scene = new Scene(root);
                // optionally add a stylesheet
                primaryStage.setScene(scene);
                // obtain controller
                ControllerClass controller = loader.getController();
                // set model
                controller.setModel(new InitGui());
                primaryStage.show();
            } catch(Exception e) {
                e.printStackTrace();
            }
    }
}

package controller;
import java.io.IOException;

import javafx.application.Application;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import model.InitGui;


public class ControllerClass {
    @FXML
    public TextField fxWeeks;
    public InitGui initGui;
    public void setModel(InitGui initGui) {
        this.initGui = initGui;
    }
    public ControllerClass () {
        fxWeeks.setText(initGui.getExample());
    }
}

package model;
import javafx.fxml.FXML;
import javafx.scene.control.TextField;
public class InitGui {
    public String getExample () {
        return "Hello";
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<Pane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="450" prefWidth="450" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="com.controller.ControllerClass">
    <MenuBar fx:id="menuBar">
        <menus>
            <Menu text="Datei">
               <MenuItem text="Öffnen"/>
               <MenuItem text="Speichern"/>
               <MenuItem text="Speichern unter"/>
               <SeparatorMenuItem  />
               <MenuItem text="Schließen"/>
            </Menu>
        </menus>
    </MenuBar>
    <children>
       <TableView fx:id="fxTable" layoutX="10.0" layoutY="75.0" prefHeight="410.0" prefWidth="600.0"/>
       <Label fx:id="fxLabel" layoutX="630.0" layoutY="60.0" Text="Kalenderwoche"/>
       <TextField fx:id="fxWeek" layoutX="630.0"  layoutY="75.0" prefWidth="95.0"/>
       <Button fx:id="fxButton" layoutX="630.0" layoutY="125.0" Text="Arbeitszeit berechnen"/>
       <Label fx:id="fxAlllbl" layoutX="10.0" layoutY="500.0" Text="Gesamt :"/>
       <TextField fx:id="fxAllContent" layoutX="80.0" layoutY="497.0"/>
   </children>
</Pane>

public class Main extends Application {
@Override
public void start(Stage primaryStage) {
    try {
        FXMLLoader loader = new FXMLLoader(getClass().getResource("fxmlFileName.fxml"));
        BorderPane root = loader.load();
        Scene scene = new Scene(root);
        // optionally add a stylesheet
        scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
        primaryStage.setScene(scene);
        // obtain controller
        ControllerClass controller = loader.getController();
        // set model
        controller.setModel(new Model());
        primaryStage.show();
    } catch(Exception e) {
        e.printStackTrace();
    }
}

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