EVENT HANDLING

Event:
Event is an object that describes a state change in a source. It can be generated as a consequence of a person interacting with the elements in a graphical user interface some of the activities that cause events to be generated are pressing a button , entering a character via the keyboard , selecting an item in a list, and clicking the mouse .

Event source: Asource is an object that generates an event.This occurs when the inernal state of that object changes in some way ,Sources may generate more than one type of event. Asource must register listeners inorder for the listeners to receive notifications about a specific type of event. Each type of event has its own registration method.

Syntax for registration method.

public void addTypeListeners(TypeListener eliment)

All registered listeners are notified and require a copy of event object. This is called multicasting.
The general form to unregister the listeners
public void removeListener(typeListeners eliment)

Event listeners:
A listener is an object that is notified when an event occurs several interfaces are found in java.awt.event.
EVENT CLASSES

ActionEvent	Generated when a button is pressed list of item is doubleclicked menuitem is selected. Constructors: ActionEvent(object,int,int) ActionEvent(object,int,string,int) Methods getActionCommand( ); getModifiers( )
AdjustmentEvent	Generated when a scrollbar is manipulated Constructor: AdjustementEvent(src,int,int,int) Methods getAdjustmentType() getValue()
ComponentEvent	It is generated when the size,position,visibility of a component is changed. Constructor: ComponentEvent(Component src,int type); Methods getComponent()
ContainerEvent	It is generated when a component is added or removed from a container . Constructor: ContainerEvent(Component src,int type,componet comp) Methods: getContainer() getChaild()
FocusEvent	It is generated when a component gains or loses input focus. Constructor: FocusEvent(Component src,int type) FocusEvent(Component src ,int type , Boolean flag) Methods isTemporary()
InputEvent	It is a subclass of component event and is the superclass for component input events. it’s subclases are KeyEvent and MouseEvent. Methods isAltDown() isAltGraphDown() isControlDown() isMetaDown() isShiftDown() getModifiers()
ItemEvent	It is generated when a checkbox or a list item is clicked or when a check menu item is selected or deselected . Constructors ItemEvent(itemselectable src,int type,object entry,int state) Methods getItem() getItemSelectable() getStateChange()
KeyEvent	It is generated when keyboard input occurs. Constructors KeyEvent(Component src,int type,long when,int modifiers,int code) KeyEvent(Component src,int type,long when,int modifiers,int code,char ch) Methods getKeyChar() getKeyCode()
MouseEvent	Generated when the mouse is dragged,moved,clicked,pressed or released. Constructors MouseEvent(component src,int type,long when,int modifiers,int x,int y,int clicks,Boolean trigger) Methods getx( ) gety( ) getpoint( ) transalatepoint(x,y) getclickcount( )
TextEvent	Instance of this class is describe text events. These are generated by text fields and text areas when characters are entered by user or program . TextEvent(Object src, int type)
WindowEvent	Window event is a subclass of ComponentEvent and has this constructor. Constructor: WindowEvent(Window src,int type) Methods getWindow()

SOURCE OF EVENTS

Button	Generated ActionEvent when a button is pressed.
Checkbox	Generates item events when the check box is selected or deselected..
Choice	Generates item events when the choice is changed
List	Generates action event when an item is doubleclicked . generates item event when an item is selected or deselected.
MenuItem	Generates action event when a menu item is selected. generates item events when a checkable menu item is selected or deselected.
Scrollbar	Generates adjustment event when the scroll bar is manipulated.
Text component	Generates text events when the user enters a character.
Window	Generates window events when a window is activated ,closed , deactivated , deiconified, iconified ,opened or quit.

EVENT LISTENER INTERFACES

ActionListener	Defines one method to receive action events Methods void actionPerformed(ActioonEvent ae)
AdjustmentListener	Defines one method to receive adjustment events Methods void adjustmentValueChanged(AdjustmentEvent ae)
ComponentListener	Defines four methods to recognize when a component is hidden , moved, resized or shown. Methods void componentResized(Component ce) void componentMoved(Component ce) void componentShown(Component ce) void componentHidden(Component ce)
ContainerListener	Defines two methods to recognize when a component is added to or removed from a container. Methods void componentAdded(ContainerEvent ce) void componentRemoved(ContainerEvent ce)
FocusListener	Defines two methods to recognize when a component gains or loses keboard focus. Methods void focusGained(FocusEvent fe) void focusLost(FocusEvent fe)
ItemListener	Defines one method to recognize when the state of an item changes. Methods void itemStateChanged(ItemEvent ie)
KeyListener	Defines three methods to recognize when a key is pressed , released or typed. Methods void keyPressed(KeyEvent ke) void keyReleased(KeyEvent ke) void keyTyped(KeyEvent ke)
MouseListener	Defines five methods to recognize when the mouse is clicked , enters a component, exits a component , is pressed , or is released. Methods void mouseClicked(MouseEvent me) void mouseEntered(MouseEvent me) void mouseExited(MouseEvent me) void mousePressed(MouseEvent me) void mouseReleased(MouseEvent me)
MouseMotionListener	Defines two methods to recognize when the mouse is dragged or moved. Methods void mouseDragged(MouseEvent me) void mouseMoved(MouseEvent me)
TextListener	Defines one method to recognize when a text value changes Methods void textChnaged(TextEvent te)
WindowListener	Defines seven methods to recognize when a window is activated , closed, deactivated, deiconified, iconified, opened, or quit. Methods void windowActivated(WindowEvent we) void windowClosed(WindowEvent we) void windowClosing(WindowEvent we) void windowDeactivated(WindowEvent we) void windowDeiconified(WindowEvent we) void windowIconified(WindowEvent we) void windowOpened(WindowEvent we)