Module javafx.base
Package javafx.beans.binding

Class DoubleBinding

java.lang.Object
javafx.beans.binding.NumberExpressionBase
javafx.beans.binding.DoubleExpression
javafx.beans.binding.DoubleBinding
All Implemented Interfaces:
Binding<Number>, NumberBinding, NumberExpression, Observable, ObservableDoubleValue, ObservableNumberValue, ObservableValue<Number>
public abstract class DoubleBinding
extends DoubleExpression
implements NumberBinding
Base class that provides most of the functionality needed to implement a Binding of a double value.

DoubleBinding provides a simple invalidation-scheme. An extending class can register dependencies by calling bind(Observable...). If One of the registered dependencies becomes invalid, this DoubleBinding is marked as invalid. With unbind(Observable...) listening to dependencies can be stopped.

To provide a concrete implementation of this class, the method computeValue() has to be implemented to calculate the value of this binding based on the current state of the dependencies. It is called when get() is called for an invalid binding.

Below is a simple example of a DoubleBinding calculating the square- root of a ObservableNumberValue moo. 

 
 final ObservableDoubleValue moo = ...;

 DoubleBinding foo = new DoubleBinding() {

     {
         super.bind(moo);
     }

     @Override
     protected double computeValue() {
         return Math.sqrt(moo.getValue());
     }
 };
Following is the same example with implementations for the optional methods Binding.getDependencies() and Binding.dispose(). 
 
 final ObservableDoubleValue moo = ...;

 DoubleBinding foo = new DoubleBinding() {

     {
         super.bind(moo);
     }

     @Override
     protected double computeValue() {
         return Math.sqrt(moo.getValue());
     }

     @Override
     public ObservableList<?> getDependencies() {
         return FXCollections.singletonObservableList(moo);
     }

     @Override
     public void dispose() {
         super.unbind(moo);
     }
 };
Since:
JavaFX 2.0
See Also:
Binding, NumberBinding, DoubleExpression

  • Constructor Details

    • DoubleBinding

      public DoubleBinding()
      Creates a default DoubleBinding.

  • Method Details

    • addListener

      public void addListener​(InvalidationListener listener)
      Description copied from interface: Observable
      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.

      Specified by:
      addListener in interface Observable
      Parameters:
      listener - The listener to register
      See Also:
      Observable.removeListener(InvalidationListener)

    • removeListener

      public void removeListener​(InvalidationListener listener)
      Description copied from interface: Observable
      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.

      Specified by:
      removeListener in interface Observable
      Parameters:
      listener - The listener to remove
      See Also:
      Observable.addListener(InvalidationListener)

    • addListener

      public void addListener​(ChangeListener<? super Number> listener)
      Description copied from interface: ObservableValue
      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.

      Specified by:
      addListener in interface ObservableValue<Number>
      Parameters:
      listener - The listener to register
      See Also:
      ObservableValue.removeListener(ChangeListener)

    • removeListener

      public void removeListener​(ChangeListener<? super Number> listener)
      Description copied from interface: ObservableValue
      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.

      Specified by:
      removeListener in interface ObservableValue<Number>
      Parameters:
      listener - The listener to remove
      See Also:
      ObservableValue.addListener(ChangeListener)

    • bind

      protected final void bind​(Observable... dependencies)
      Start observing the dependencies for changes. If the value of one of the dependencies changes, the binding is marked as invalid.
      Parameters:
      dependencies - the dependencies to observe

    • unbind

      protected final void unbind​(Observable... dependencies)
      Stop observing the dependencies for changes.
      Parameters:
      dependencies - the dependencies to stop observing

    • dispose

      public void dispose()
      A default implementation of dispose() that is empty.
      Specified by:
      dispose in interface Binding<Number>

    • getDependencies

      public ObservableList<?> getDependencies()
      A default implementation of getDependencies() that returns an empty ObservableList.
      Specified by:
      getDependencies in interface Binding<Number>
      Returns:
      an empty ObservableList

    • get

      public final double get()
      Returns the result of computeValue(). The method computeValue() is only called if the binding is invalid. The result is cached and returned if the binding did not become invalid since the last call of get().
      Specified by:
      get in interface ObservableDoubleValue
      Returns:
      the current value

    • onInvalidating

      protected void onInvalidating()
      The method onInvalidating() can be overridden by extending classes to react, if this binding becomes invalid. The default implementation is empty.

    • invalidate

      public final void invalidate()
      Description copied from interface: Binding
      Mark a binding as invalid. This forces the recalculation of the value of the Binding next time it is request.
      Specified by:
      invalidate in interface Binding<Number>

    • isValid

      public final boolean isValid()
      Description copied from interface: Binding
      Checks if a binding is valid.
      Specified by:
      isValid in interface Binding<Number>
      Returns:
      true if the Binding is valid, false otherwise

    • computeValue

      protected abstract double computeValue()
      Calculates the current value of this binding.

      Classes extending DoubleBinding have to provide an implementation of computeValue.

      Returns:
      the current value

    • toString

      public String toString()
      Returns a string representation of this DoubleBinding object.
      Overrides:
      toString in class Object
      Returns:
      a string representation of this DoubleBinding object.