Developing Java Beans

Bound Properties

In the previous example, property changes can take place when one of the setStocks() methods are invoked. This results in the state of the WatchList being changed. What would happen if two objects were using the WatchList and one of them changed the Stocks property? It’s possible that users of the WatchList will want to know if its properties are changed.

A Bean component can provide change notifications for its properties. These notifications take the form of events, and they conform to the event model described in the earlier chapters. Properties that support change notifications are known as bound properties, because other objects can bind themselves to changes in their value.

Non-Specific Property Binding

An object can bind itself to non-specific property changes. In this case the source object sends notifications to the bound object whenever the value of one of its bound properties has changed. The notification takes the form of a java.beans.PropertyChangeEvent. The public methods for this class are shown below, without their implementations:

public class java.beans.PropertyChangeEvent extends java.util.EventObject { // contructor PropertyChangeEvent(Object source, // the source of the event String propertyName, // the property name Object oldValue, // the old value Object newValue); // the new value // get the new value of the property public Object getNewValue(); // get the old value of the property public Object getOldValue(); // get the event propagation ...