# Interface ChangeListener<T>

Type Parameters:
  `T` - the observable value type

All Known Implementing Classes:
  `WeakChangeListener`

Functional Interface:
  This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface public interface ChangeListener<T>
A `ChangeListener` is notified whenever the value of an `ObservableValue` changes. It can be registered and unregistered with `ObservableValue.addListener(ChangeListener)` respectively `ObservableValue.removeListener(ChangeListener)`

For an in-depth explanation of change events and how they differ from invalidation events, see the documentation of `ObservableValue`.

The same instance of `ChangeListener` can be registered to listen to multiple `ObservableValues`.

Since:
  JavaFX 2.0
See Also:
  - `ObservableValue`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `changed(ObservableValue<? extends T> observable, T oldValue, T newValue)`
  Called when the value of an `ObservableValue` changes.

- ## Method Details

  - ### changed

    void changed(ObservableValue<? extends T> observable, T oldValue, T newValue)
    Called when the value of an `ObservableValue` changes.

    In general, it is considered bad practice to modify the observed value in this method.

    Parameters:
      `observable` - The `ObservableValue` which value changed
      `oldValue` - The old value
      `newValue` - The new value