Differs from its superclass
PropertyChangeSupport
in that it can
check for changed values using
#equals
or
==
.
Useful if you want to ensure that a
PropertyChangeEvent
is fired
if the old and new value are not the same but if they are equal.
The
Java
Bean Secification recommends to not throw a
PropertyChangeEvent if the old and new value of a bound
Bean property are equal (see chapter 7.4.4). This can reduce the number
of events fired and helps avoid loops. Nevertheless a bound property
may fire an event if the old and new value are equal.
An example for a condition where the identity check
==
is required and the
#equals
test fails is class
SelectionInList
. If the contained
ListModel
changes its value, an internal listener is removed
from the old value and added to the new value. The listener must be
moved from the old instance to the new instance even if these are equal.
The
PropertyChangeSupport
doesn't fire a property change event
if such a
ListModel
is implemented as a
java.util.List
.
This is because instances of
List
are equal if and only if
all list members are equal and if they are in the same sequence.
This class provides two means to fire an event if the old and new
value are equal but not the same. First, you enable the identity check
in constructor
ExtendedPropertyChangeSupport(Object,boolean)
.
By default all calls to
#firePropertyChange
will then
check the identity, not the equality. Second, you can invoke
firePropertyChange(PropertyChangeEvent,boolean)
or
firePropertyChange(String,Object,Object,boolean)
and
enable or disable the identity check for this call only.
TODO: (Issue #5) Use WeakReferences to refer to registered listeners.
TODO: (Issue #6) Add an optional check for valid property name
when adding a listener for a specific property.
TODO: (Issue #7) Add an optional strict check for existing
property names when firing a named property change.
TODO: (Issue #8) Add an option to ensure that update notifications
are performed in the event dispatch thread. In case a bean
is changed in a thread other than the event dispatch thread, such
a feature would help complying with Swing's single thread rule.
TODO: (Issue #11) Consider adding an option that saves update notifications
if 'checkIdentity' is true but the value types can be compared
safely via #equals, for example Strings, Booleans and Numbers.
firePropertyChange
public void firePropertyChange(PropertyChangeEvent evt)
Fires the specified PropertyChangeEvent to any registered listeners.
Uses the default test (#equals
vs. ==
)
to determine whether the event's old and new values are different.
No event is fired if old and new value are the same.
evt
- The PropertyChangeEvent object.
PropertyChangeSupport.firePropertyChange(PropertyChangeEvent)
firePropertyChange
public void firePropertyChange(PropertyChangeEvent evt,
boolean checkIdentity)
Fires an existing PropertyChangeEvent to any registered listeners.
The boolean parameter specifies whether differences between the old
and new value are tested using ==
or #equals
.
No event is fired if old and new value are the same.
evt
- The PropertyChangeEvent object.checkIdentity
- true to check differences using ==
false to use #equals
.
firePropertyChange
public void firePropertyChange(String propertyName,
Object oldValue,
Object newValue)
Reports a bound property update to any registered listeners.
Uses the default test (#equals
vs. ==
)
to determine whether the event's old and new values are different.
No event is fired if old and new value are the same.
propertyName
- The programmatic name of the property
that was changed.oldValue
- The old value of the property.newValue
- The new value of the property.
PropertyChangeSupport.firePropertyChange(String, Object, Object)
firePropertyChange
public void firePropertyChange(String propertyName,
Object oldValue,
Object newValue,
boolean checkIdentity)
Reports a bound property update to any registered listeners.
No event is fired if the old and new value are the same.
If checkIdentity is true
an event is fired in all
other cases. If this parameter is false
, an event is fired
if old and new values are not equal.
propertyName
- The programmatic name of the property
that was changed.oldValue
- The old value of the property.newValue
- The new value of the property.checkIdentity
- true to check differences using ==
false to use #equals
.