EDU.oswego.cs.dl.util.concurrent

Class VetoableChangeMulticaster

Implemented Interfaces:
Serializable

public class VetoableChangeMulticaster
extends java.lang.Object
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. ]

Field Summary

protected HashMap
children
HashMap for managing listeners for specific properties.
protected VetoableChangeListener[]
listeners
The array of listeners.
protected Object
source
The object to be provided as the "source" for any generated events.

Constructor Summary

VetoableChangeMulticaster(Object sourceBean)
Constructs a VetoableChangeMulticaster object.

Method Summary

void
addVetoableChangeListener(String propertyName, VetoableChangeListener listener)
Add a VetoableChangeListener for a specific property.
void
addVetoableChangeListener(VetoableChangeListener listener)
Add a VetoableChangeListener to the listener list.
void
addVetoableChangeListenerIfAbsent(String propertyName, VetoableChangeListener listener)
Add a VetoableChangeListener for a specific property, if it is not already registered.
void
addVetoableChangeListenerIfAbsent(VetoableChangeListener listener)
Add a PropertyChangeListener to the listener list if it is not already present.
void
fireVetoableChange(PropertyChangeEvent evt)
Report a vetoable property update to any registered listeners.
void
fireVetoableChange(String propertyName, Object oldValue, Object newValue)
Report a vetoable property update to any registered listeners.
void
fireVetoableChange(String propertyName, boolean oldValue, boolean newValue)
Report a vetoable property update to any registered listeners.
void
fireVetoableChange(String propertyName, int oldValue, int newValue)
Report a vetoable property update to any registered listeners.
protected VetoableChangeMulticaster
getChild(String propertyName)
Return the child associated with property, or null if no such
boolean
hasListeners(String propertyName)
Check if there are any listeners for a specific property.
protected void
multicast(PropertyChangeEvent evt)
Helper method to relay evt to all listeners.
void
removeVetoableChangeListener(String propertyName, VetoableChangeListener listener)
Remove a VetoableChangeListener for a specific property.
void
removeVetoableChangeListener(VetoableChangeListener listener)
Remove an occurrence of a VetoableChangeListener from the listener list.

Field Details

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.

Constructor Details

VetoableChangeMulticaster

public VetoableChangeMulticaster(Object sourceBean)
Constructs a VetoableChangeMulticaster object.
Parameters:
sourceBean - The bean to be given as the source for any events.

Method Details

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.
Parameters:
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.
Parameters:
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.
Parameters:
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.
Parameters:
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.

Parameters:
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.

Parameters:
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.

Parameters:
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.

Parameters:
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.
Parameters:
propertyName - the property name.
Returns:
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.
Parameters:
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.
Parameters:
listener - The VetoableChangeListener to be removed