Why can't I use the same Image twice? - javafx

Question

I have been trying to learn more on using JavaFX and in this program I am trying to display a 3 by 3 game of tic tac toe that has already been played. I have created my ImageViews and set the images I want to use but once I started plugging them into columns and rows I noticed I cannot use the same one twice. I have an image for an empty space, an X, and an O. Once I use one more than once I get an "Exception while running application". Might be a rookie mistake, but an explanation would be greatly appreciated.
package Fresh;
import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;
public class Fresh extends Application {
#Override
public void start(Stage primaryStage) {
//Create a pane and set its properties
GridPane pane = new GridPane();
pane.setAlignment(Pos.CENTER);
pane.setPadding(new Insets(11.5, 12.5, 13.5, 14.5));
pane.setHgap(5.5);
pane.setVgap(5.5);
//imv0 = X image
final ImageView imv0 = new ImageView();
final Image image0 = new Image(Fresh.class.getResourceAsStream("images/x.gif"));
imv0.setImage(image0);
//imv1 = O image
final ImageView imv1 = new ImageView();
final Image image1 = new Image(Fresh.class.getResourceAsStream("images/o.gif"));
imv1.setImage(image1);
//imv2 = empty image
final ImageView imv2 = new ImageView();
final Image image2 = new Image(Fresh.class.getResourceAsStream("images/empty.gif"));
imv2.setImage(image2);
//Place nodes in the pane
pane.add((imv0),0,0);
pane.add((imv1), 1, 0);
//Once I try to use imv0 again "I get an exception while running".
pane.add((imv0),0,1);
//Create a scene and place it in the stage
Scene scene = new Scene(pane);
primaryStage.setTitle("ShowGridPane");
primaryStage.setScene(scene);
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}

Answer 1

You can use the same Image as many times as you like; however, you can only place a given ImageView in one place in the scene graph. From the Javadocs:
A node may occur at most once anywhere in the scene graph.
To see why this must be true, what would you expect
GridPane.getColumnIndex(imv0)
to return, given the code you have?
So you can do:
final Image image0 = new Image(Fresh.class.getResourceAsStream("images/x.gif"));
ImageView imv00 = new ImageView(image0);
ImageView imv01 = new ImageView(image0);
pane.add(imv00, 0, 0);
pane.add(imv01, 0, 1);
// etc
The overhead here is not too bad; you use the same image data for each ImageView.