Programming Java Concept of Event Handling

Prepared By: Asst. Prof. Sejal Jadav
1

Unit-5
CS – 19 : Programming with Java
UNIT – 5
GUI using SWING, Event Handling
B.C.A & B.SC.(IT) – 4

Event Handling
Unit-5(Part-2)

Event Classes
and
Listener Interfaces

Event Classes Listener Interfaces
ActionEvent ActionListener
ItemEvent ItemListener
FocusEvent FocusListener
MouseEvent MouseListener and MouseMotionListener
MouseWheelEvent MouseWheelListener
TextEvent TextListener
KeyEvent KeyListener

Q-8 Explain FocusEvent Class.
• A FocusEvent is generated when a component gains or loses input
focus.
FOCUS_GAINED
• It is set when the component gains the input focus.
FOCUS_LOST
• It is set when the component loses the input focus.

• FocusEvent is a subclass of ComponentEvent and has these
constructors:
• FocusEvent(Component src, int type)
• FocusEvent(Component src, int type, boolean temporaryFlag)
• Here, src is a reference to the component that generated this event. The type
of the event is specified by type. The argument temporaryFlag is set to true if
the focus event is temporary. Otherwise, it is set to false.

• (A temporary focus event occurs as a result of another user interface
operation.
• For example, assume that the focus is in a text field. If the user moves
the mouse to adjust a scroll bar, the focus is temporarily lost.)

• The isTemporary( ) method indicates if this focus change is temporary.
Its form is shown here:
boolean isTemporary( )
• The method returns true if the change is temporary. Otherwise, it
returns false.

Q: 15 The FocusListener Interface:
• This interface defines two methods which are called when a component
gets or loses the focus.
void focusGained(FocusEvent fe)
void focusLost(FocusEvent fe)
• Example: AwtListenerDemo.java

Q: Java Adapter Classes
• Java adapter classes provide the default implementation of listener
interfaces.
• If you inherit the adapter class, you will not be forced to provide the
implementation of all the methods of listener interfaces.
• So it saves code.

Swing Focus Adapter
• 1. FocusAdapter class is an abstract adapter class in Java Swing.
• 2. FocusAdapter class is for receiving keyboard focus events.
• 3. Methods specified in FocusAdapter class are empty.
• 4. FocusAdapter class exists as convenience(suitable) for creating
listener objects

Class declaration
• Below is the declaration for java.awt.event.FocusAdapter class –
public abstract class FocusAdapter extends Object
implements FocusListener

Class constructors: FocusAdapter()
Class methods:
No. Method Return Type Parameter Invoked when
1 focusGained() void FocusEvent
component gains the
keyboard focus
2 focusLost() void FocusEvent
component loses the
keyboard focus

Methods inherited:
• This class inherits methods from the following classes:
java.lang.Object
Swing Focus Adapter Example: AdapterExample.java

Q-10 Explain KeyEvent Class.
• A KeyEvent is generated when keyboard input occurs. There are three
types of key events, which are identified by these integer constants:
KEY_PRESSED
• It is set when a key is pressed in the keyboard.
KEY_RELEASED
• It is set when a key is pressed in the keyboard.

KEY_TYPED
• It is set when a printable key is pressed. The key such as ALT, CTRL,
SHIFT, etc are not printable character.

• There are many other integer constants that are defined by KeyEvent.
For example, VK_0 through VK_9 and VK_A through VK_Z define the
ASCII equivalents of the numbers and letters.
• Here are some others:

Here are some others:
• The VK constants specify virtual key codes and are independent of any
modifiers, such as control, shift, or alt.
VK_ENTER VK_ESCAPE VK_CANCEL
VK_UP VK_DOWN VK_LEFT
VK_RIGHT VK_PAGE_DOWN
VK_PAGE_UP VK_SHIFT VK_ALT
VK_CONTROL

• KeyEvent is a subclass of InputEvent. Here are two of its 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)

• Here, src is a reference to the component that generated the event. The
type of the event is specified by type.
• The system time at which the key was pressed is passed in when.
• The modifiers argument indicates which modifiers were pressed when
this key event occurred.

• The virtual key code, such as VK_UP, VK_A, and so forth, is passed in
code.
• The character equivalent (if one exists) is passed in ch.
• If no valid character exists, then ch contains CHAR_UNDEFINED.
• For KEY_TYPED events, code will contain VK_UNDEFINED.

The most commonly used methods of KeyEvent class are:
char getKeyChar( )
• It returns the character that was pressed entered.
getKeyCode( )
• It returns the code of the key pressed.

Q: 15) The KeyListener Interface:
• This interface defines three methods.
void keyPressed(KeyEvent ke)
• This method is called when a keyboard key is pressed.
void keyReleased(KeyEvent ke)
• This method is called when a keyboard key is released.
void keyTyped(KeyEvent ke)
• This method is called when a printable character key is pressed.

• Example: KeyEvents.java

Java KeyAdapter Example [page- 24]
• The class KeyAdapter is an abstract (adapter) class for receiving
keyboard events.
• All methods of this class are empty. This class is convenience class for
creating listener objects.

 Class declaration
• Following is the declaration for java.awt.event.KeyAdapter class:
public abstract class KeyAdapter
extendsObject
implements KeyListener
• Example: KeyAdapterExample.java

Q-11 Explain MouseEvent Class.
• There are seven types of mouse events.
• The MouseEvent class defines the following integer constants that can be
used to identify them:
MOUSE_CLICKED
• The user clicked the mouse.
MOUSE_DRAGGED
• The user dragged the mouse.

MOUSE_ENTERED
• The mouse entered a component.
MOUSE_EXITED
• The mouse exited from a
component.
MOUSE_MOVED
• The mouse moved.
MOUSE_PRESSED
• The mouse was pressed.
MOUSE_RELEASED
• The mouse was released.

• MouseEvent is a subclass of InputEvent.
Here is one of its constructors.
MouseEvent(Component src, int type, long when, int modifiers, int x, int
y, int clickCount, boolean opensPopup)

MouseEvent(Component src, int type, long when, int
modifiers, int x, int y, int clickCount, boolean opensPopup)
• Here, src is a reference to the component that generated the event.
• The type is the type of the event and time specifies the system time at which the event was
generated.
• The modifiers parameter specifies any modifier keys that were pressed during the event.
• The x and y are the coordinates of the mouse location.
• The clickCount stores the number of mouse click.
• When opensPopup is true, it specifies that any popup menu was opened after the mouse
event.

• The commonly used methods of MouseEvent are:
int getX( )
• It returns the x coordinate of the mouse cursor.
int getY( )
• It returns the y coordinate of the mouse cursor.

void translatePoint(int x, int y)
• It translate the mouse pointer to specified x and y location.
int getClickCount( )
• It returns the number of mouse pointer clicked. For example 2 for double
click.
boolean isPopupTrigger( )
• It returns the true if any popup was opened after the mouse event.

Q: 15 ) The MouseListener Interface:
• This interface defines five methods which are called when a mouse event is
generated These methods are:
void mouseClicked(MouseEvent me)
• This method is called when the mouse button is clicked.
void mouseEntered(MouseEvent me)
• This method is called when the mouse button is entered into a component.

void mouseExited(MouseEvent me)
• This method is called when the mouse button is exited from a component.
void mousePressed(MouseEvent me)
• This method is called when the mouse button is pressed.
void mouseReleased(MouseEvent me)
• This method is called when the mouse button is released.

Q: 15) The MouseMotionListener Interface:
• This interface defines two methods.
void mouseDragged(MouseEvent me)
• This method is called the mouse is dragged.
void mouseMoved(MouseEvent me)
• This method is called when mouse pointer is moved.

Q-15) The MouseWheelListener Interface:
• It has one method:
void mouseWheelMoved(MouseWheelEvent mwe)
• This method is called when the wheel of the mouse is moved.
• Example: Q-16 Mouse Handling Program:
• MouseEvents.java

Q: Java MouseAdapter Example [page: 23]
• The class MouseAdapter is an abstract (adapter) class for receiving
mouse events.

• Class declaration:
• Following is the declaration for java.awt.event.MouseAdapter class:
Public abstract class MouseAdapter extends Object
implements
MouseListener,MouseWheelListener,MouseMotionListener

• Example: MouseAdapterExample.java

Q: Java MouseMotionAdapter Example [page:23]
• The class MouseMotionAdapter is an abstract (adapter) class for
receiving mouse motion events.

 Class Declaration
• Following is the declaration for java.awt.event.MouseMotionAdapter
class −
public abstract class MouseMotionAdapter
extends Object
implements MouseMotionListener
• Example:MouseMotionAdapterExample.java

Q-12 Explain TextEvent Class.
• The TextEvent is generated when user inputs some text into a text field or a
text area. It has one integer constant.
TEXT_VALUE_CHANGED
• It is set when the text in a text field or a text area changed.
• Its constructor is: TextEvent(Object source,int type)
• Here source is the object that generated this event.
• The type is the type event which can be TEXT_VALUE_CHANGED.

Q:15) The TextListener Interface:
• This interface ha one method:
void textChanged(TextEvent te)
• It is called when the text of a text area or text field is changed.
• Example: JavaExampleTextEvent.java

Q-13 Explain WindowEvent Class.
• The WindowEvent class handles the events related to a window and it is
a subclass of ComponentEvent class.
• There are ten types of window events constant:
WINDOW_ACTIVATED
• The window was activated.

WINDOW_DEACTIVATED
• The window was deactivated.
WINDOW_CLOSED
• The window has been closed.
WINDOW_CLOSING
• The user requested that the window be closed.

WINDOW_OPENED
• The window was opened.
WINDOW_GAINED_FOCUS
• The window gained input focus.
WINDOW_LOST_FOCUS
• The window lost input focus.

WINDOW_ICONIFIED
• The window was iconified. Ex it is minimized
WINDOW_DEICONIFIED
• The window was deiconified. Ex it is restored
WINDOW_STATE_CHANGED
• It is set when the state of the window is changed.

• The constructors of WindowEvent are:
• WindowEvent(Window source, int type)
• WindowEvent(Window source, int type, Window other)
• WindowEvent(Window source, int type, int oldState, int newState)
• WindowEvent(Window source, int type, Window other, int oldState, int
newState)

• Here, source is the window object that generated the window event.
• The type specifies the type of event such as WINDOW_CLOSING etc.
• The other specifies the opposite window when a focus event occurs.
• The oldState is the previous state of the event.
• The newState is the new state of the window.

 The methods of WindowEvent are:
Window getWindow( )
• It returns the Window object that generated window the event.
Window getOppositeWindow()
• It returns the opposite window that a focus event has been generated.

int getOldState()
• It returns the previous state of the window.
int getNewState()
• It returns the new state of the window.

Q:15) The WindowListener Interface:
• This interface has seven methods.
void windowActivated(WindowEvent we)
• This method is called when the window is activated.
void windowDeactivated(WindowEvent we)
• This method is called when the window is deactivated.

void windowClosed(WindowEvent we)
• This method is called when the window has been closed.
void windowClosing(WindowEvent we)
• This method is called when the window is being closed.
void windowOpened(WindowEvent we)
• This method is called when the window has been opened.

void windowIconified(WindowEvent we)
• This method is called when the window is minimized.
void windowDeiconified(WindowEvent we)
• This method is called when the window is restored.
• Example: WindowExample.java

Q: 15) The WindowFocusListener Interface:
void windowGainedFocus(WindowEvent we)
• This is called when a window gains the input focus.
void windowLostFocus(WindowEvent we)
• This is called when a window loses the input focus.
• Example: WindowFocusListenerEx.java

Q: Java WindowAdapter Example [page-22]
• The class WindowAdapter is an abstract (adapter) class for receiving
window events.

 Class declaration
• Following is the declaration for java.awt.event.WindowAdapter class:
Public abstract class WindowAdapter
Extends Object
Implements
WindowListener,WindowStateListener,WindowFocusListener

• Dispose(): method :JFrame window to be destroyed and cleaned up by
the operating system.
• Example: AdapterExample1.java

Q-14 Explain Source of Events.
• Source of events are:
Button
• It generates action events (ActionEvent class) when the button is pressed.
Checkbox
• It generates item events (ItemEvent class) when the check box is checked or
unchecked.

Choice
• It generates item events (ItemEvent class) when the item is changed in the
choice.
List
• It can generateaction events as well as item events.When an item is double-
clicked, it generates ActionEvent and it generates ItemEvent when an item is
selected or deselected in the list.

Menu Item
• It can generate action events as well as item events. It generates action events
when an menu item is selected from a menu and generates an item event
when a checkable menu item is selected or deselected.
Scrollbar
• It generates adjustment events (AdjustmentEvent class) when the scroll bar
is adjusted.

Text controls such as text field, text area
• It generates text events when the user enters a character into text field
or text area.
Window
• It generates window events when a window is activated, opened, closed
etc.

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Programming Java Concept of Event Handling

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