The java.awt.event package contains many event classes which can be used for event handling.
Root class for all the event classes in Java is EventObject which is available in java.util package.
Root class for all AWT event classes is AWTEvent which is available in java.awt package and is a sub class of EventObject class.
Some of the frequently used event classes available in java.awt.eventpackage are listed below:
Various constructors and methods available in the above listed event classes are as follows:
ActionEvent
An action event is generated when a button is clicked, or a list item is double-clicked, or a menu item is selected.
ActionEvent class contains the following methods:
String getActionCommand() – Used to obtain the command name for the invoking ActionEvent object.
int getModifiers() – This method returns an integer that indicates which modifier keys (ALT, CTRL, META, and/or SHIFT) were pressed.
long getWhen() – Returns the time when the event was generated.
AdjustmentEvent
The adjustment event is generated when the scroll bar is adjusted. There are five types of adjustment events. For each type there is a constant declared in the class which are as follows:
BLOCK_DECREMENT
BLOCK_INCREMENT
TRACK
UNIT_DECREMENT
UNIT_INCREMENT
Following are the methods available in AdjustmentEvent class:
Adjustable getAdjustable() – Returns the object that generated the event.
int getAdjustmentType() – Returns one of the five constants that represents the type of event.
int getValue() – Returns a number that represents the amount of adjustment.
ComponentEvent
A component event is generated when the visibility, position and size of a component is changed. There are four types of component events which are identified by the following constants:
COMPONENT_HIDDEN
COMPONENT_SHOWN
COMPONENT_MOVED
COMPONENT_RESIZED
Following method is available in the ComponentEvent class:
Component getComponent() – Returns the component that generated the event.
ContainerEvent
A container event is generated when a component is added to or removed from the container. There are two types of container events which are represented by the following constants:
COMPONENT_ADDED
COMPONENT_REMOVED
Following are the methods available in the ContainerEvent class:
Container getContainer() – Returns the reference of the container that generated the event.
Component getChild() – Returns the reference of the component that is added to or removed from the container.
FocusEvent
A focus event is generated when a component gains or loses input focus. These events are identified by the following constants:
FOCUS_GAINED
FOCUS_LOST
Following are the methods available in the FocusEvent class:
Component getOppositeComponent() – Returns the other component that gained or lost focus.
boolean isTemporary() – Method returns true or false that indicates whether the change in focus is temporary or not.
ItemEvent
An item event is generated when the user clicks on a check box or clicks a list item or selects / deselects a checkable menu item. These events are identified by the following constants:
SELECTED
DESELECTED
Following are the methods available in the ItemEvent class:
Object getItem() – Returns a reference to the item whose state has changed.
ItemSelectable getItemSelectable() – Returns the reference of ItemSelectableobject that raised the event.
int getStateChange() – Returns the status of the state (whether SELECTED or DESELECTED)
KeyEvent
A key event is generated when a key on the keyboard is pressed, released or typed. These events are identified by the following constants:
KEY_PRESSED (when a key is pressed)
KEY_RELEASED (when a key is released)
KEY_TYPED (when a character is typed)
There are several other constants which recognizes various keys on the keyboard and they are as follows:
KeyEvent is a sub class of InputEvent. Following are the methods available in KeyEvent class:
char getKeyChar() – Returns the character entered from the keyboard
int getKeyCode() – Returns the key code
MouseEvent
The mouse event is generated when the user generates a mouse event on a source. Mouse events are represented by the following constants:
Following are some of the methods available in MouseEvent class:
int getX() – Returns the x-coordinate of the mouse at which the event was generated.
int getY() – Returns the y-coordinate of the mouse at which the event was generated.
Point getPoint() – Returns the x and y coordinates of mouse at which the event was generated.
int getClickCount() – This method returns the number of mouse clicks for an event.
int getButton() – Returns an integer that represents the buttons that caused the event. Returned value can be either NOBUTTON, BUTTON1 (left mouse button), BUTTON2 (middle mouse button), or BUTTON3 (right mouse button).
Following methods are available to obtain the coordinates relative to the screen:
Point getLocationOnScreen()
int getXOnScreen()
int getYOnScreen()
TextEvent
The text event is generated when the user enters a character into a text field or a text area. This event is identified by the following constant:
TEXT_VALUE_CHANGED
WindowEvent
A window event is generated when a user performs any one of the window related events which are identified by the following constants:
Following are some of the methods available in the WindowEvent class:
Window getWindow() – Returns the reference of the window on which the event is generated.
Window getOppositeWindow() – Returns the reference to the previous window when a focus event of activation event has occurred.
int getOldState() – Returns an integer indicating the old state of the window.
int getNewState() – Returns an integer indicating the new state of the window.
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