Working with event handling


Posted in : Core Java Posted on : October 25, 2010 at 6:51 PM Comments : [ 0 ]
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This section contains the detail about theevent handling in java Swing.

Working with event handling

? An object that describes a change of state in a source component is called an event.
? The source components can be the elements of the Graphical User Interface(GUI).
? Events are supported by the classes and interfaces defined in the 'java.awt.event' package.
? Identifying the Source Of Events:
? An event source is an object that generates an event.
? An event source registers some listeners, which receive notifications about a specific type of event generated by that particular event source.
? All the registered listeners are notified about the generation of an event and receive a copy of the event object.
? This is known as multicasting the event.
? Some sources allow only single listener to register.
? This is known as unicasting of event.

Given below various event sources and the types of events they generate :

Event Source    Description    
Checkbox Creates an item event when a check
box is selected or deselected.
Button Creates an action event when a
button is pressed.
List Creates an action event when an item
is double-clicked; creates an item
event when an item is selected or
deselected.
Scrollbar Creates an adjustment event when
a scroll bar is scrolled.
Text components Creates a text event when a text
character is entered in the text
component.
Window Creates a window event when a
window is activated, deactivated,
opened, closed, or quit.

Event Listeners and Event Handlers

? An event listener listens for a specific event and is notified when that specific event occurs.
? An event listener registers with one or more event sources to receive notifications about specific types of events and processes the events.
? An event-handler is called by the event listener whenever a specific event occurs.
? Event listeners are interfaces and the event-handler is a method declared in the event listener interface that is implemented by the application.
? The syntax of a method that registers an event listener with an event source is:
   public void addTYPEListener(TYPEListener obj)

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