Module javafx.base
Package javafx.beans

# Interface Observable

All Known Subinterfaces:
  `Binding<T>`, `JavaBeanProperty<T>`, `NumberBinding`, `NumberExpression`, `ObservableArray<T>`, `ObservableBooleanValue`, `ObservableDoubleValue`, `ObservableFaceArray`, `ObservableFloatArray`, `ObservableFloatValue`, `ObservableIntegerArray`, `ObservableIntegerValue`, `ObservableList<E>`, `ObservableListValue<E>`, `ObservableLongValue`, `ObservableMap<K,V>`, `ObservableMapValue<K,V>`, `ObservableNumberValue`, `ObservableObjectValue<T>`, `ObservableSet<E>`, `ObservableSetValue<E>`, `ObservableStringValue`, `ObservableValue<T>`, `Property<T>`, `ReadOnlyJavaBeanProperty<T>`, `ReadOnlyProperty<T>`, `TextInputControl.Content`, `WritableListValue<E>`, `WritableMapValue<K,V>`, `WritableSetValue<E>`

All Known Implementing Classes:
  `BooleanBinding`, `BooleanExpression`, `BooleanProperty`, `BooleanPropertyBase`, `DoubleBinding`, `DoubleExpression`, `DoubleProperty`, `DoublePropertyBase`, `FilteredList`, `FloatBinding`, `FloatExpression`, `FloatProperty`, `FloatPropertyBase`, `IntegerBinding`, `IntegerExpression`, `IntegerProperty`, `IntegerPropertyBase`, `JavaBeanBooleanProperty`, `JavaBeanDoubleProperty`, `JavaBeanFloatProperty`, `JavaBeanIntegerProperty`, `JavaBeanLongProperty`, `JavaBeanObjectProperty`, `JavaBeanStringProperty`, `ListBinding`, `ListExpression`, `ListProperty`, `ListPropertyBase`, `LongBinding`, `LongExpression`, `LongProperty`, `LongPropertyBase`, `MapBinding`, `MapExpression`, `MapProperty`, `MapPropertyBase`, `ModifiableObservableListBase`, `NumberExpressionBase`, `ObjectBinding`, `ObjectExpression`, `ObjectProperty`, `ObjectPropertyBase`, `ObservableArrayBase`, `ObservableListBase`, `ObservableValueBase`, `ReadOnlyBooleanProperty`, `ReadOnlyBooleanPropertyBase`, `ReadOnlyBooleanWrapper`, `ReadOnlyDoubleProperty`, `ReadOnlyDoublePropertyBase`, `ReadOnlyDoubleWrapper`, `ReadOnlyFloatProperty`, `ReadOnlyFloatPropertyBase`, `ReadOnlyFloatWrapper`, `ReadOnlyIntegerProperty`, `ReadOnlyIntegerPropertyBase`, `ReadOnlyIntegerWrapper`, `ReadOnlyJavaBeanBooleanProperty`, `ReadOnlyJavaBeanDoubleProperty`, `ReadOnlyJavaBeanFloatProperty`, `ReadOnlyJavaBeanIntegerProperty`, `ReadOnlyJavaBeanLongProperty`, `ReadOnlyJavaBeanObjectProperty`, `ReadOnlyJavaBeanStringProperty`, `ReadOnlyListProperty`, `ReadOnlyListPropertyBase`, `ReadOnlyListWrapper`, `ReadOnlyLongProperty`, `ReadOnlyLongPropertyBase`, `ReadOnlyLongWrapper`, `ReadOnlyMapProperty`, `ReadOnlyMapPropertyBase`, `ReadOnlyMapWrapper`, `ReadOnlyObjectProperty`, `ReadOnlyObjectPropertyBase`, `ReadOnlyObjectWrapper`, `ReadOnlySetProperty`, `ReadOnlySetPropertyBase`, `ReadOnlySetWrapper`, `ReadOnlyStringProperty`, `ReadOnlyStringPropertyBase`, `ReadOnlyStringWrapper`, `SetBinding`, `SetExpression`, `SetProperty`, `SetPropertyBase`, `SimpleBooleanProperty`, `SimpleDoubleProperty`, `SimpleFloatProperty`, `SimpleIntegerProperty`, `SimpleListProperty`, `SimpleLongProperty`, `SimpleMapProperty`, `SimpleObjectProperty`, `SimpleSetProperty`, `SimpleStringProperty`, `SimpleStyleableBooleanProperty`, `SimpleStyleableDoubleProperty`, `SimpleStyleableFloatProperty`, `SimpleStyleableIntegerProperty`, `SimpleStyleableLongProperty`, `SimpleStyleableObjectProperty`, `SimpleStyleableStringProperty`, `SortedList`, `StringBinding`, `StringExpression`, `StringProperty`, `StringPropertyBase`, `StyleableBooleanProperty`, `StyleableDoubleProperty`, `StyleableFloatProperty`, `StyleableIntegerProperty`, `StyleableLongProperty`, `StyleableObjectProperty`, `StyleableStringProperty`, `TransformationList`

public interface Observable
An `Observable` is an entity that wraps content and allows to observe the content for invalidations.

An implementation of `Observable` may support lazy evaluation, which means that the content is not immediately recomputed after changes, but lazily the next time it is requested. All bindings and properties in this library support lazy evaluation.

Implementations of this class should strive to generate as few events as possible to avoid wasting too much time in event handlers. Implementations in this library mark themselves as invalid when the first invalidation event occurs. They do not generate anymore invalidation events until their value is recomputed and valid again.

Since:
  JavaFX 2.0
See Also:
  - `ObservableValue`
  - `ObservableList`
  - `ObservableMap`

## Method Summary

Modifier and Type
Method
Description
`void`
`addListener(InvalidationListener listener)`
Adds an `InvalidationListener` which will be notified whenever the `Observable` becomes invalid.
`void`
`removeListener(InvalidationListener listener)`
Removes the given listener from the list of listeners, that are notified whenever the value of the `Observable` becomes invalid.

## Method Details

### addListener

void addListener(InvalidationListener listener)
Adds an `InvalidationListener` which will be notified whenever the `Observable` becomes invalid. If the same listener is added more than once, then it will be notified more than once. That is, no check is made to ensure uniqueness.

Note that the same actual `InvalidationListener` instance may be safely registered for different `Observables`.

The `Observable` stores a strong reference to the listener which will prevent the listener from being garbage collected and may result in a memory leak. It is recommended to either unregister a listener by calling `removeListener` after use or to use an instance of `WeakInvalidationListener` avoid this situation.

Parameters:
  `listener` - The listener to register
Throws:
  `NullPointerException` - if the listener is null
See Also:
  - `removeListener(InvalidationListener)`

### removeListener

void removeListener(InvalidationListener listener)
Removes the given listener from the list of listeners, that are notified whenever the value of the `Observable` becomes invalid.

If the given listener has not been previously registered (i.e. it was never added) then this method call is a no-op. If it had been previously added then it will be removed. If it had been added more than once, then only the first occurrence will be removed.

Parameters:
  `listener` - The listener to remove
Throws:
  `NullPointerException` - if the listener is null
See Also:
  - `addListener(InvalidationListener)`