I've been working arround a GUI in Vaadin, with some given classes from my IT chief. It's all great and that, but, today, I have encountered that I cannot use a lambda expression in a addListener method type. This method is custom, as the object that uses it. Here is the implementation:
public class ResetButtonForTextField extends AbstractExtension {
private final List<ResetButtonClickListener> listeners
= new ArrayList<ResetButtonClickListener>();
private void addResetButtonClickedListener
(ResetButtonClickListener listener) {
listeners.add(listener);
}
//Some other methods and the call of the listeners
}
public interface ResetButtonClickListener extends Serializable {
public void resetButtonClicked();
}
To use this extension you must do this:
ResetButtonForTextField rb=ResetButtonForTextField.extend(button);
rb.addResetButtonClickedListener(new ResetButtonClickListener() {
@Override
public void resetButtonClicked() {
//Do some stuff here
}
});
If I use a lambda in addResetButtonClickedListener like this:
rb.addResetButtonClickedListener(ev -> {
//Do some magic here
}
The compiler says that
Lambda expression's signature does not match the signature of the functional interface method resetButtonClicked()
The method addResetButtonClickedListener(ResetButtonClickListener) in the type ResetButtonForTextField is not applicable for the arguments (( ev) -> {})
Even if I define lambda expression like this: (ResetButtonClickListener ev) -> {} still gives an error.
So question is, Why can't I use a lambda expression there? I'm missing something in the declaration of the code?
The functional interface consists of the method
public void resetButtonClicked()
with no parameters. Your lambda tries to implement it with a parameter of type ResetButtonClickListener. What you want to do is
rb.addResetButtonClickedListener(() -> {
// handling code goes here
});