928: Mainline

Components, such as JPanel instances and instances of JPanel subclasses, support a marvelous mechanism for activating connected property-change listeners.

The mechanism, in overview, works as follows:

• The firePropertyChange method, called on a component, activates each connected property-change listener by calling the listener's propertyChange method.
• The propertyChange method does whatever you like; typically, the propertyChange method fetches values from views and relays those values to models.
• The addPropertyChangeListener method connects property-change listeners to the components in which calls to the firePropertyChange method occur.