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Properties of Beans
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Is subset of a component state
are aspects of a Bean’s appearance and
behavior that are changeable at design
time
are private values accessed through get
and set methods
Simple Properties
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Contains one value that may be either
a simple type or a object
Property get and set method names
follow specific rules called design
patterns
Using design pattern-based method names,
JavaBeans-enabled builder tools can
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Discover a Bean’s properties
Determine the properties read/write attributes
Determine the properties type
Locate an appropriate property editor for each
property type
Display the properties(usually in a property
sheet)
Alter those properties(at design time)
Naming patterns
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public T getN()
public void setN(T value)
T is the type of the property and N is its name
A property typically has these both of these
methods
a read-only property has only the getN() method
a write-only property has only the setN() method
Boolean Properties
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Contains one value that may be either true or
false
Naming patterns
to read the property
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to write the property
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public boolean isN()
public boolean getN()
public void setN(boolean value)
N is the name of the property
Indexed Properties
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Contains several values that may be either
simple types or objects
Represent collection of values accessed by
index
public T getN(int index)
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T is the type and N is its name
reads one value where index identifies which
entry is wanted
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public T[] getN()
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public void setN(int index, T value)
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All values may be retrieved
writes one value
the argument index identifies which entry to
change, and the argument value is the new value
for that property
public void setN(T values[])
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All values may be updated
the argument values is an array that contains the
new values for the property
Bound Property
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Allow one bean to notify other components
about relevant changes to its prperties
When a bound property is changed, a
property change event is multicast to other
beans to inform them of this update
convenient mechanism to communicate a
change in the property among a set of
components
PropertyChangeEvent class
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In java.beans package
defines the event notifications that are multicast
by a bean when one of its bound properties is
changed
PrpertyChangeEvent( Objetc src, String pname,
Object oValue, Object nValue)
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src is the bean whose property has changed
pname - the name of the property
oValue, nValue - old and new values of the property
Methods
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Object getNewValue()
returns an Object with the new value of the
property
Object getOldValue()
 returns an Object with old value of the property
String getPropertyName()
 returns the string equivalent of the property
name
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PropertyChangeListener interface
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In the java.beans package
to receive PropertyChangeEvent
notifications
defines one method
void propertyChange
(PropertyChangeEvent pce)
PropertyChangeSupport class
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In java.beans package
used to perform much of the work associated
with bound properties
PropertyChangeSupport(Object src)
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src is the bean whose bound property is changed
synchronized void addPropertyChangeListener
(PropertyChangeListener pcl)
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method registers the listener for property change
events
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synchronized void
removePropertyChangeListener(
PropertyChangeListener pcl)
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method unregisters the listener for property change
events
void firePropertyChange(String pname, Object
oldValue, Object newValue)
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Via this method A property change notification is
multicast to the listeners
pname - the name of the property
oldValue, newValue - old and new values of that
property
Constrained Properties
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When a constrained property is changed, an
event notification can be multicast to other
Beans to inform them of the proposed
modification
the listeners may accept the update
it is also possible for one or more listeners
to veto the change
in that case, the source receives an
exception and restores the property to its
old value
VetoableChangeListener interface
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In the java.beans package
used to receive PropertyChangeEvent
notification when constrained properties are
changed
defines one method
void vetoableChange(PropertyChangeEvent pce)
throws PropertyVetoException
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implementation of this method should throw an
exception if it wants to reject the property change
PropertyVetoException class
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In the java.beans package
PropertyVetoException(String message,
PropertyChangeEvent pce)
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message - is a String that is presented to the
user if the property change is rejected
pce - is a reference to the
PropertyChangeEvent object
VetoableChangeSupport class
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In the java.beans package
used to perform much of the work associated
with constrained properties
VetoableChangeSupport(Object src)
 src - is the bean whose constrained
property is changed
Methods
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synchronized void addVetoableChangeListener
(VetoableChangeListener pcl)
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register the listener for property change events
associated with constrained properties
synchronized void
removeVetoableChangeListener
(VetoableChnageListener pcl)
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unregister the listener for property change events
associated with constrained properties
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Void fireVetoableChange(String pname,
Object oldValue, Object newValue) throws
PropertyVetoException
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method multicasts a notification about a
property change to the listeners
pname - name of the property
oldValue, newValue - the old and new values
of the property