Unhandled Exception Error when I have already thrown the errors in the method

Question

I am trying to set a mouse event on mouse realeased for a button in javafx. The program is attached to an excel file which reads in the button data. When I use the event to give it a method it saying unhandled error excpetion whe I have already thrown the errors in both methods.

@FXML
void initRecipes() throws IOException, InvalidFormatException {

    File file = new File("src/main/resources/RecipeList/Recipes.xlsx");
    String path = file.getAbsolutePath();
    ExcelReader list = new ExcelReader(path);

    int i = 10;
    int sheetNo = 0;

        categories.add(cheap);
        categories.add(showstopper);
        categories.add(quick);
        categories.add(breakfast);
        categories.add(deserts);
        categories.add(salads);

        for (HBox h : categories) {
            for (int k = 0; k < list.getAmount(sheetNo); k++) {

                String buttonId = Integer.toString(i) + Integer.toString(k + 1);
                Button button = new Button(list.getName(buttonId, sheetNo));
                button.setId(buttonId);
                button.setStyle("-fx-background-image: url('" + 
                list.getImage(buttonId, sheetNo) + "')");
                button.setPrefHeight(buttonHeight);
                button.setPrefWidth(buttonWidth);

                button.setOnMouseReleased(event -> changeScene(buttonId));
                 //Error occuring here ^^^^^
                h.getChildren().add(button);
            }

            sheetNo++;
            i += 10;

        }
        list.close();
    }

void changeScene(String buttonId) throws IOException, InvalidFormatException {

    File file = new File("src/main/resources/RecipeList/ingredients.xlsx");
    String path = file.getAbsolutePath();

    ExcelReader list = new ExcelReader(path);

    SecondaryPresenter s = new SecondaryPresenter();
    s.initialize();


}

I'm quite unsure if this is the correct way to set up an event and why it is showing this error if I have already thrown the 2 errors it says I haven't handled. Does anyone know what I'm doing wrong? Thanks

Answer 1

The signature of EventHandler<T>.handle is

void handle​(T event)

Since your changeScene has a throws clause containing exceptions that are not RuntimeExceptions, the java compiler determines that these kind of exceptions are not handled in your lambda expression. The lambda expression results in a very similar result as the following code:

button.setOnMouseReleased(new EventHandler<MouseEvent>() {
    @Override
    public void handle(MouseEvent event) {
        changeScene(buttonId);
    }
});

In the code above it should be easy to see that the handle method does not handle the exceptions thrown by changeScene properly.

You need to add a try/catch to the body of the lambda expression:

button.setOnMouseReleased(event -> {
    try {
        changeScene(buttonId);
    } catch (IOException | InvalidFormatException ex) {
        // TODO: exception handling
    }
});