一応ここにも置いておきます。
ランダムに画像が出て3コマ漫画になる。

--->kadai_randomcomic.java

package application;

import javafx. application.Application;
import javafx.event.ActionEvent;
import javafx.geometry.Pos;
import javafx. scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.control.Button;
import javafx.scene.image.Image;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx. stage.Stage;

public class kadai_randomcomic extends Application {
 Image[] myImage = new Image[12];
 int boxX = 300;
 int boxY = 180;

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

 @Override

 public void start(Stage myStage) {
  Canvas canvas = new Canvas(300,600);
  GraphicsContext gc = canvas.getGraphicsContext2D();

  BorderPane pane = new BorderPane();
  pane.setStyle("-fx-background-color:white;");

  //画像に関して

  myImage[0] = new Image("img1.png");
  myImage[1] = new Image("img2.png");
  myImage[2] = new Image("img3.png");
  myImage[3] = new Image("img4.png");
  myImage[4] = new Image("img5.png");
  myImage[5] = new Image("img6.png");
  myImage[6] = new Image("img7.png");
  myImage[7] = new Image("img8.png");
  myImage[8] = new Image("img9.png");
  myImage[9] = new Image("img10.png");
  myImage[10] = new Image("img11.png");
  myImage[11] = new Image("img12.png");

  //ボタンに関して

  Button btn01 = new Button("random comic start");

  btn01.setOnAction((ActionEvent event)->{
   int ran = (int)(Math.random()*3);//ランダム
   int ran2 = (int)(Math.random()*5+3);
   int ran3 = (int)(Math.random()*4+8);
   System.out.println("ran is"+ran);
   gc.drawImage(myImage[ran], 0, 0, boxX, boxY);
   gc.drawImage(myImage[ran2], 0, 200, boxX, boxY);
   gc.drawImage(myImage[ran3], 0, 400, boxX, boxY);

  });

  HBox hbox = new HBox();
  hbox.getChildren().addAll(btn01);
  hbox.setAlignment(Pos.CENTER);

  pane.setTop(hbox);
  pane.setCenter(canvas);

  Scene scene = new Scene(pane,300,600);
  myStage.setTitle("Exe28 random comic");
  myStage.setScene(scene);
  myStage.show();
 }
}