Controller.java

package sample;

import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;

import java.io.File;
import java.util.Random;

public class Controller {

    Random random = new Random();

    @FXML
    private ImageView diceImage;

    @FXML
    private Button rollButton;

    @FXML
    void roll(ActionEvent event) {

        rollButton.setDisable(true);

        Thread thread = new Thread(){
            public void run(){
                System.out.println("Thread Running");
                try {
                    for (int i = 0; i < 15; i++) {
                        File file = new File("src/sample/dice/dice" + (random.nextInt(6)+1)+".png");
                        diceImage.setImage(new Image(file.toURI().toString()));
                        Thread.sleep(50);
                    }
                    rollButton.setDisable(false);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };

        thread.start();
    }
}

Main.java

package sample;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
        primaryStage.setTitle("Hello World");
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
    }


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

sample.fxml

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

<?import javafx.scene.control.Button?>
<?import javafx.scene.image.Image?>
<?import javafx.scene.image.ImageView?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.text.Font?>

<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/15.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
   <children>
      <ImageView fx:id="diceImage" fitHeight="200.0" fitWidth="200.0" layoutX="92.0" layoutY="100.0" pickOnBounds="true" preserveRatio="true">
         <image>
            <Image url="@dice/dice1.png" />
         </image></ImageView>
      <Button fx:id="rollButton" layoutX="379.0" layoutY="163.0" mnemonicParsing="false" onAction="#roll" text="Roll">
         <font>
            <Font size="35.0" />
         </font></Button>
   </children>
</AnchorPane>