08_Exception

Code-Dateien

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CODECode_Bank.zipDownload
CODECode_Pizza.zipDownload
CODECode_Urlaub.zipDownload

Videos

DateinameAktion
VIDEOVideo_Bank_DAbspielen
VIDEOVideo_Pizza_EAbspielen
VIDEOVideo_Urlaub_DAbspielen

Lernmaterialien

Exception

Button

OrdersView.java

    private final Button buttonAddWrong = new Button("Add WRONG order");

        public OrdersView(@Autowired PizzaOrderService pizzaOrderService) {} {
            buttonAddWrong.addClickListener(b -> addWrongOrder());
        }

        private void addWrongOrder() {
            pizzaOrderService.addWrongOrder();
            reload();
        }

PizzaOrderService.java

    public void addWrongOrder() {
        PizzaOrder order;

        // -20 Euro!!!
        order = new PizzaOrder(LocalDate.now(), "Margherita", "Large", -20.0, 1, true);
        orders.add(order);
    }

PizzaOrder.java

    public void setPrice(Double price) throws PizzaOrderException {
        if (price < 8)
            throw new PizzaOrderException("The min. price is 8.0 Eur");
        if (price > 30)
            throw new PizzaOrderException("The max. price is 30.0 Eur");

        this.price = price;
    }

PizzaOrderException.java

public class PizzaOrderException extends RuntimeException {
    public PizzaOrderException(String message) {
        super(message);
    }
}

Here is a short explanation of what your code does and where the issue is:

OrdersView (UI layer)

private final Button buttonAddWrong = new Button("Add WRONG order");
  • Creates a button in the UI.
buttonAddWrong.addClickListener(b -> addWrongOrder());
  • When the button is clicked → calls addWrongOrder().
private void addWrongOrder() {
    pizzaOrderService.addWrongOrder();
    reload();
}

  • Calls the service to add an invalid order

  • Then refreshes the Grid

PizzaOrderService (business logic)

order = new PizzaOrder(..., -20.0, ...);
orders.add(order);

  • Creates a pizza order with price = -20 € ❌

  • Adds it to the list

👉 This is intentionally invalid data

PizzaOrder (validation)

public void setPrice(Double price) throws PizzaOrderException {
    if (price < 8)
        throw new PizzaOrderException("The min. price is 8.0 Eur");

  • Validates the price

  • Throws an exception if:

    • price < 8

    • price > 30

👉 So -20 should trigger an exception

PizzaOrderException

public class PizzaOrderException extends RuntimeException

  • Custom exception

  • Extends RuntimeException → unchecked exception

  • No try/catch required → app can crash if not handled

Error Message

OrdersView.java

private void addWrongOrder() {
    try {
        pizzaOrderService.addWrongOrder();
        reload();
    }
    catch (PizzaOrderException e) {
        Notification.show(e.getMessage());
    }
}

Method is called

This method is usually triggered by your button:

buttonAddWrong.addClickListener(b -> addWrongOrder());

👉 User clicks → this method runs

try { ... } block

pizzaOrderService.addWrongOrder();

  • Calls the service

  • Service tries to create an invalid order (price = -20)

👉 This may throw a PizzaOrderException

reload();

  • Only runs if no exception occurred

  • Refreshes the Grid

catch (PizzaOrderException e)

If something goes wrong:

catch (PizzaOrderException e)

  • Catches your custom exception

  • Prevents the app from crashing

Show error message

Notification.show(e.getMessage());

  • Displays the error text from the exception

  • Example message:

    The min. price is 8.0 Eur

👉 User sees feedback instead of a broken UI

001.png

Dialog

    ConfirmDialog dialog = new ConfirmDialog();
    dialog.setHeader("Error");
    dialog.setText(e.getMessage());
    dialog.setConfirmText("OK");
    dialog.open();

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