propertyChangePropertyChangeEvent

PropertyChangeEvent is a class in the JavaBeans API that represents a notification about a change to a bean’s bound property. It is used to inform listeners that a property value has changed from an old value to a new value.

The event carries details about the change, including the source object that fired the event, the name of the property that changed, and the previous and new values. Specifically, a PropertyChangeEvent typically provides accessors for the source, property name, old value, and new value through methods like getSource(), getPropertyName(), getOldValue(), and getNewValue(). A common constructor accepts the four pieces of information: the source object, the property name, the old value, and the new value.

PropertyChangeEvent is part of the JavaBeans binding mechanism. Beans that expose bound properties typically maintain a list of PropertyChangeListeners and notify them when a property changes by creating and firing a PropertyChangeEvent. The notification is usually performed via a helper such as PropertyChangeSupport, which aggregates listeners and handles the dispatch of events to all registered listeners.

Listeners interested in property changes implement the PropertyChangeListener interface, which requires the propertyChange(PropertyChangeEvent evt) method. In the event handler, listeners examine evt.getPropertyName() and react to changes accordingly, often updating user interfaces or triggering related business logic.

In addition to PropertyChangeEvent, Java also supports indexed property changes through IndexedPropertyChangeEvent for properties that are array- or list-like. Overall, PropertyChangeEvent is a foundational element for decoupled, event-driven property binding in Java. See also PropertyChangeSupport, PropertyChangeListener, and IndexedPropertyChangeEvent.