Module javafx.base
Package javafx.beans.value

Interface ObservableValue<T>

Type Parameters:
T - The type of the wrapped value.
All Superinterfaces:
Observable
All Known Subinterfaces:
Binding<T>, JavaBeanProperty<T>, NumberBinding, NumberExpression, ObservableBooleanValue, ObservableDoubleValue, ObservableFloatValue, ObservableIntegerValue, ObservableListValue<E>, ObservableLongValue, ObservableMapValue<K,​V>, ObservableNumberValue, ObservableObjectValue<T>, ObservableSetValue<E>, ObservableStringValue, Property<T>, ReadOnlyJavaBeanProperty<T>, ReadOnlyProperty<T>, TextInputControl.Content
All Known Implementing Classes:
BooleanBinding, BooleanExpression, BooleanProperty, BooleanPropertyBase, DoubleBinding, DoubleExpression, DoubleProperty, DoublePropertyBase, 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, NumberExpressionBase, ObjectBinding, ObjectExpression, ObjectProperty, ObjectPropertyBase, 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, StringBinding, StringExpression, StringProperty, StringPropertyBase, StyleableBooleanProperty, StyleableDoubleProperty, StyleableFloatProperty, StyleableIntegerProperty, StyleableLongProperty, StyleableObjectProperty, StyleableStringProperty
public interface ObservableValue<T>
extends Observable
An ObservableValue is an entity that wraps a value and allows to observe the value for changes. In general this interface should not be implemented directly but one of its sub-interfaces (ObservableBooleanValue etc.).

The value of the ObservableValue can be requested with getValue().

An implementation of ObservableValue may support lazy evaluation, which means that the value is not immediately recomputed after changes, but lazily the next time the value is requested (see note 1 in "Implementation Requirements").

An ObservableValue generates two types of events: change events and invalidation events. A change event indicates that the value has changed (see note 2 in "Implementation Requirements"). An invalidation event is generated if the current value is not valid anymore. This distinction becomes important if the ObservableValue supports lazy evaluation, because for a lazily evaluated value one does not know if an invalid value really has changed until it is recomputed. For this reason, generating change events requires eager evaluation while invalidation events can be generated for eager and lazy implementations.

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 any more invalidation events until their value is recomputed and valid again.

Two types of listeners can be attached to an ObservableValue: InvalidationListener to listen to invalidation events and ChangeListener to listen to change events.

Important note: attaching a ChangeListener enforces eager computation even if the implementation of the ObservableValue supports lazy evaluation.

Implementation Requirements:
  1. All bindings and properties in the JavaFX library support lazy evaluation.
  2. All implementing classes in the JavaFX library check for a change using reference equality (and not object equality, Object#equals(Object)) of the value.
Since:
JavaFX 2.0
See Also:
ObservableBooleanValue, ObservableDoubleValue, ObservableFloatValue, ObservableIntegerValue, ObservableLongValue, ObservableNumberValue, ObservableObjectValue, ObservableStringValue

  • Method Summary

    Modifier and Type Method Description
    void addListener​(ChangeListener<? super T> listener)
    Adds a ChangeListener which will be notified whenever the value of the ObservableValue changes.
    T getValue()
    Returns the current value of this ObservableValue
    void removeListener​(ChangeListener<? super T> listener)
    Removes the given listener from the list of listeners that are notified whenever the value of the ObservableValue changes.

    Methods declared in interface javafx.beans.Observable

    addListener, removeListener

  • Method Details

    • addListener

      void addListener​(ChangeListener<? super T> listener)
      Adds a ChangeListener which will be notified whenever the value of the ObservableValue changes. 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 ChangeListener instance may be safely registered for different ObservableValues.

      The ObservableValue 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 WeakChangeListener avoid this situation.

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

    • removeListener

      void removeListener​(ChangeListener<? super T> listener)
      Removes the given listener from the list of listeners that are notified whenever the value of the ObservableValue changes.

      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(ChangeListener)

    • getValue

      T getValue()
      Returns the current value of this ObservableValue
      Returns:
      The current value