EDU.oswego.cs.dl.util.concurrent
Class VetoableChangeMulticaster
- Serializable
public class VetoableChangeMulticaster
implements Serializable
This class is interoperable with java.beans.VetoableChangeSupport,
but relies on a streamlined copy-on-write scheme similar to
that used in CopyOnWriteArrayList. It also adheres to clarified
semantics of add, remove, and fireVetoableChange operations.
Sample usage.
class Thing {
protected Color myColor = Color.red; // an example property
protected boolean changePending; // track whether in midst of change
// vetoable listeners:
protected VetoableChangeMulticaster vetoers =
new VetoableChangeMulticaster(this);
// Possibly also some ordinary listeners:
protected PropertyChangeMulticaster listeners =
new PropertyChangeMulticaster(this);
// registration methods, including:
void addVetoer(VetoableChangeListener l) {
// Use the `ifAbsent' version to avoid duplicate notifications
vetoers.addVetoableChangeListenerIfAbsent(l);
}
public synchronized Color getColor() { // accessor
return myColor;
}
// Simple transactional control for vetos
public void setColor(int newColor) throws PropertyVetoException {
Color oldColor = prepareSetColor(newColor);
try {
vetoers.fireVetoableChange("color", oldColor, newColor);
commitColor(newColor);
listeners.firePropertyChange("color", oldColor, newColor);
}
catch(PropertyVetoException ex) {
abortSetColor();
throw ex;
}
}
// Called on entry to proposed vetoable change from setColor.
// Throws exception if there is already another change in progress.
// Returns current color
synchronized int prepareSetColor(Color c) throws PropertyVetoException {
// only support one transaction at a time
if (changePending)
throw new PropertyVetoException("Concurrent modification");
// (Could alternatively wait out other transactions via
// a wait/notify construction based on changePending.)
// perhaps some other screenings, like:
else if (c == null)
throw new PropertyVetoException("Cannot change color to Null");
else {
changePending = true;
return myColor;
}
}
synchronized void commitColor(Color newColor) {
myColor = newColor;
changePending = false;
}
synchronized void abortSetColor() {
changePending = false;
}
}
[
Introduction to this package. ]
protected HashMap | children - HashMap for managing listeners for specific properties.
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protected VetoableChangeListener[] | listeners - The array of listeners.
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protected Object | source - The object to be provided as the "source" for any generated events.
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void | addVetoableChangeListener(String propertyName, VetoableChangeListener listener) - Add a VetoableChangeListener for a specific property.
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void | addVetoableChangeListener(VetoableChangeListener listener) - Add a VetoableChangeListener to the listener list.
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void | addVetoableChangeListenerIfAbsent(String propertyName, VetoableChangeListener listener) - Add a VetoableChangeListener for a specific property, if it is not
already registered.
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void | addVetoableChangeListenerIfAbsent(VetoableChangeListener listener) - Add a PropertyChangeListener to the listener list if it is
not already present.
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void | fireVetoableChange(PropertyChangeEvent evt) - Report a vetoable property update to any registered listeners.
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void | fireVetoableChange(String propertyName, Object oldValue, Object newValue) - Report a vetoable property update to any registered listeners.
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void | fireVetoableChange(String propertyName, boolean oldValue, boolean newValue) - Report a vetoable property update to any registered listeners.
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void | fireVetoableChange(String propertyName, int oldValue, int newValue) - Report a vetoable property update to any registered listeners.
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protected VetoableChangeMulticaster | getChild(String propertyName) - Return the child associated with property, or null if no such
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boolean | hasListeners(String propertyName) - Check if there are any listeners for a specific property.
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protected void | multicast(PropertyChangeEvent evt) - Helper method to relay evt to all listeners.
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void | removeVetoableChangeListener(String propertyName, VetoableChangeListener listener) - Remove a VetoableChangeListener for a specific property.
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void | removeVetoableChangeListener(VetoableChangeListener listener) - Remove an occurrence of a VetoableChangeListener from the listener list.
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children
protected HashMap children
HashMap for managing listeners for specific properties.
Maps property names to VetoableChangeMulticaster objects.
listeners
protected VetoableChangeListener[] listeners
The array of listeners. Copied on each update
source
protected final Object source
The object to be provided as the "source" for any generated events.
VetoableChangeMulticaster
public VetoableChangeMulticaster(Object sourceBean)
Constructs a VetoableChangeMulticaster
object.
sourceBean
- The bean to be given as the source for any events.
addVetoableChangeListener
public void addVetoableChangeListener(String propertyName,
VetoableChangeListener listener)
Add a VetoableChangeListener for a specific property. The listener
will be invoked only when a call on fireVetoableChange names that
specific property. However, if a listener is registered both for all
properties and a specific property, it will receive multiple
notifications upon changes to that property.
propertyName
- The name of the property to listen on.listener
- The VetoableChangeListener to be added
addVetoableChangeListener
public void addVetoableChangeListener(VetoableChangeListener listener)
Add a VetoableChangeListener to the listener list.
The listener is registered for all properties.
If the listener is added multiple times, it will
receive multiple change notifications upon any fireVetoableChange.
listener
- The VetoableChangeListener to be added
addVetoableChangeListenerIfAbsent
public void addVetoableChangeListenerIfAbsent(String propertyName,
VetoableChangeListener listener)
Add a VetoableChangeListener for a specific property, if it is not
already registered. The listener
will be invoked only when a call on fireVetoableChange names that
specific property.
propertyName
- The name of the property to listen on.listener
- The VetoableChangeListener to be added
addVetoableChangeListenerIfAbsent
public void addVetoableChangeListenerIfAbsent(VetoableChangeListener listener)
Add a PropertyChangeListener to the listener list if it is
not already present.
The listener is registered for all properties.
The operation maintains Set semantics: If the listener is already
registered, the operation has no effect.
listener
- The PropertyChangeListener to be added
fireVetoableChange
public void fireVetoableChange(PropertyChangeEvent evt)
throws PropertyVetoException
Report a vetoable property update to any registered listeners.
Notifications are sent serially (although in no particular order)
to the list of listeners,
aborting if one throws PropertyVetoException. Upon this exception,
fire a new event reverting this
change to all listeners that have already been notified
(ignoring any further vetos),
suppress notifications to all other listeners, and
then rethrow the PropertyVetoException.
No event is fired if old and new are equal and non-null.
equal and non-null.
evt
- The PropertyChangeEvent object.
fireVetoableChange
public void fireVetoableChange(String propertyName,
Object oldValue,
Object newValue)
throws PropertyVetoException
Report a vetoable property update to any registered listeners.
Notifications are sent serially (although in no particular order)
to the list of listeners,
aborting if one throws PropertyVetoException. Upon this exception,
fire a new event reverting this
change to all listeners that have already been notified
(ignoring any further vetos),
suppress notifications to all other listeners, and
then rethrow the PropertyVetoException.
No event is fired if old and new are equal non-null.
propertyName
- The programmatic name of the property
that was changed.oldValue
- The old value of the property.newValue
- The new value of the property.
fireVetoableChange
public void fireVetoableChange(String propertyName,
boolean oldValue,
boolean newValue)
throws PropertyVetoException
Report a vetoable property update to any registered listeners.
Notifications are sent serially (although in no particular order)
to the list of listeners,
aborting if one throws PropertyVetoException. Upon this exception,
fire a new event reverting this
change to all listeners that have already been notified
(ignoring any further vetos),
suppress notifications to all other listeners, and
then rethrow the PropertyVetoException.
No event is fired if old and new are equal.
This is merely a convenience wrapper around the more general
fireVetoableChange method that takes Object values.
propertyName
- The programmatic name of the property
that was changed.oldValue
- The old value of the property.newValue
- The new value of the property.
fireVetoableChange
public void fireVetoableChange(String propertyName,
int oldValue,
int newValue)
throws PropertyVetoException
Report a vetoable property update to any registered listeners.
Notifications are sent serially (although in no particular order)
to the list of listeners,
aborting if one throws PropertyVetoException. Upon this exception,
fire a new event reverting this
change to all listeners that have already been notified
(ignoring any further vetos),
suppress notifications to all other listeners, and
then rethrow the PropertyVetoException.
No event is fired if old and new are equal.
This is merely a convenience wrapper around the more general
fireVetoableChange method that takes Object values.
propertyName
- The programmatic name of the property
that was changed.oldValue
- The old value of the property.newValue
- The new value of the property.
getChild
protected VetoableChangeMulticaster getChild(String propertyName)
Return the child associated with property, or null if no such
hasListeners
public boolean hasListeners(String propertyName)
Check if there are any listeners for a specific property.
If propertyName is null, return whether there are any listeners at all.
propertyName
- the property name.
- true if there are one or more listeners for the given property
multicast
protected void multicast(PropertyChangeEvent evt)
throws PropertyVetoException
Helper method to relay evt to all listeners.
Called by all public fireVetoableChange methods.
removeVetoableChangeListener
public void removeVetoableChangeListener(String propertyName,
VetoableChangeListener listener)
Remove a VetoableChangeListener for a specific property.
Affects only the given property.
If the listener is also registered for all properties,
then it will continue to be registered for them.
propertyName
- The name of the property that was listened on.listener
- The VetoableChangeListener to be removed
removeVetoableChangeListener
public void removeVetoableChangeListener(VetoableChangeListener listener)
Remove an occurrence of a VetoableChangeListener from the listener list.
It removes at most one occurrence of the given listener.
If the listener was added multiple times it must be removed
mulitple times.
This removes a VetoableChangeListener that was registered
for all properties, and has no effect if registered for only
one or more specified properties.
listener
- The VetoableChangeListener to be removed