# Class PropertyChangeEvent

java.lang.Object
java.util.EventObject
java.beans.PropertyChangeEvent

All Implemented Interfaces:
  `Serializable`

Direct Known Subclasses:
  `IndexedPropertyChangeEvent`

public class PropertyChangeEvent extends EventObject
A "PropertyChange" event gets delivered whenever a bean changes a "bound" or "constrained" property. A PropertyChangeEvent object is sent as an argument to the PropertyChangeListener and VetoableChangeListener methods.

Normally PropertyChangeEvents are accompanied by the name and the old and new value of the changed property. If the new value is a primitive type (such as int or boolean) it must be wrapped as the corresponding java.lang.* Object type (such as Integer or Boolean).

Null values may be provided for the old and the new values if their true values are not known.

An event source may send a null object as the name to indicate that an arbitrary set of if its properties have changed. In this case the old and new values should also be null.

Since:
  1.1
See Also:
  - Serialized Form

- ## Field Summary

  ### Fields declared in class EventObject

  `source`

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `PropertyChangeEvent(Object source, String propertyName, Object oldValue, Object newValue)`
  Constructs a new `PropertyChangeEvent`.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `Object`
  `getNewValue()`
  Gets the new value for the property, expressed as an Object.
  `Object`
  `getOldValue()`
  Gets the old value for the property, expressed as an Object.
  `Object`
  `getPropagationId()`
  The "propagationId" field is reserved for future use.
  `String`
  `getPropertyName()`
  Gets the programmatic name of the property that was changed.
  `void`
  `setPropagationId(Object propagationId)`
  Sets the propagationId object for the event.
  `String`
  `toString()`
  Returns a string representation of the object.

  ### Methods declared in class EventObject

  `getSource`

  ### Methods declared in class Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- ## Constructor Details

  - ### PropertyChangeEvent

    public PropertyChangeEvent(Object source, String propertyName, Object oldValue, Object newValue)
    Constructs a new `PropertyChangeEvent`.
    Parameters:
      `source` - the bean that fired the event
      `propertyName` - the programmatic name of the property that was changed
      `oldValue` - the old value of the property
      `newValue` - the new value of the property
    Throws:
      `IllegalArgumentException` - if `source` is `null`

- ## Method Details

  - ### getPropertyName

    public String getPropertyName()
    Gets the programmatic name of the property that was changed.
    Returns:
      The programmatic name of the property that was changed. May be null if multiple properties have changed.

  - ### getNewValue

    public Object getNewValue()
    Gets the new value for the property, expressed as an Object.
    Returns:
      The new value for the property, expressed as an Object. May be null if multiple properties have changed.

  - ### getOldValue

    public Object getOldValue()
    Gets the old value for the property, expressed as an Object.
    Returns:
      The old value for the property, expressed as an Object. May be null if multiple properties have changed.

  - ### setPropagationId

    public void setPropagationId(Object propagationId)
    Sets the propagationId object for the event.
    Parameters:
      `propagationId` - The propagationId object for the event.

  - ### getPropagationId

    public Object getPropagationId()
    The "propagationId" field is reserved for future use. In Beans 1.0 the sole requirement is that if a listener catches a PropertyChangeEvent and then fires a PropertyChangeEvent of its own, then it should make sure that it propagates the propagationId field from its incoming event to its outgoing event.
    Returns:
      the propagationId object associated with a bound/constrained property update.

  - ### toString

    public String toString()
    Returns a string representation of the object.
    Overrides:
      `toString` in class `EventObject`
    Returns:
      a string representation of the object
    Since:
      1.7