from Component, such as Applet, can generate events. For example, you can receive key and
mouse events from an applet. (You may also build your own components that generate
events.) In this chapter, we will be handling only mouse and keyboard events, but the
following two chapters will be handling events from the sources shown in Table 22-2.
Event Listener Interfaces
As explained, the delegation event model has two parts: sources and listeners. Listeners are
created by implementing one or more of the interfaces defined by the java.awt.event package.
When an event occurs, the event source invokes the appropriate method defined by the
listener and provides an event object as its argument. Table 22-3 lists commonly used listener
interfaces and provides a brief description of the methods that they define. The following
sections examine the specific methods that are contained in each interface.
The ActionListener Interface
This interface defines the actionPerformed( ) method that is invoked when an action event
occurs. Its general form is shown here:
void actionPerformed(ActionEvent ae)
Interface
Description
ActionListener
Defines one method to receive action events.
AdjustmentListener
Defines one method to receive adjustment events.
ComponentListener
Defines four methods to recognize when a component is hidden,
moved, resized, or shown.
ContainerListener
Defines two methods to recognize when a component is added to
or removed from a container.
FocusListener
Defines two methods to recognize when a component gains or loses
keyboard focus.
ItemListener
Defines one method to recognize when the state of an item changes.
KeyListener
Defines three methods to recognize when a key is pressed, released,
or typed.
MouseListener
Defines five methods to recognize when the mouse is clicked, enters
a component, exits a component, is pressed, or is released.
MouseMotionListener
Defines two methods to recognize when the mouse is dragged or
moved.
MouseWheelListener
Defines one method to recognize when the mouse wheel is moved.
TextListener
Defines one method to recognize when a text value changes.
WindowFocusListener
Defines two methods to recognize when a window gains or loses
input focus.
WindowListener
Defines seven methods to recognize when a window is activated,
closed, deactivated, deiconified, iconified, opened, or quit.
TABLE 22-3
Commonly Used Event Listener Inter faces
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