How do I write a new ListChangeListener<Item>() with lambda?

java lambda listener java-8 changelistener
simonides picture simonides · Apr 28, 2014 · Viewed 19.9k times · Source

How do I write a new ListChangeListener() with lambda in java8?

listItems.addListener(new ListChangeListener<Item>() {
    @Override
    public void onChanged(
        javafx.collections.ListChangeListener.Change<? extends Item> c) {
        // TODO Auto-generated method stub
    }
});

This is what I tried:

listItems.addListener(c->{});

But eclipse states:

The method addListener(ListChangeListener) is ambiguous for the type ObservableList.

The List is declared as:

ObservableList<Item> listItems = FXCollections.observableArrayList();

Answer

Andrew Vitkus picture Andrew Vitkus · Apr 28, 2014

Since ObservableList inherits addListener(InvalidationListener) from the Observable interface, the compiler is unable to determine which version to call. Specifying the type of the lambda through a cast should fix this.

listItems.addListener((ListChangeListener)(c -> {/* ... */}));

You can also explicitly specify the type of c:

listItems.addListener((ListChangeListener.Change<? extends Item> c) -> {/* ... */});

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