An event is defined as the act of changing the state of an item or behavior. A button click, cursor movement, key press via keyboard, or page scrolling are all examples of actions.

Various event classes can be found in the java.awt.event package.

Event Handling Components:

There are three major components to event management.

• An event is a change in the state of an item.
• An object that generates an event is referred to as an event source.
• Listeners are objects that pay attention to an event. When an event occurs, a listener is notified.

How are Events Handled?

A source generates an Event and sends it to one or more registered listeners. When the listener receives an event, it processes it and returns. Several Java packages, including java.util, java.awt, and java.awt.event, support events.

Event Classes in Java:

Event Class	Listener Interface	Description
ActionEvent	ActionListener	An event that signals the occurrence of a component-defined action, such as a button click or the selection of an item from the menu-item list.
AdjustmentEvent	AdjustmentListener	An Adjustable object, such as a Scrollbar, emits the adjustment event.
ComponentEvent	ComponentListener	An Adjustable object, such as a Scrollbar, emits the adjustment event. An event that indicates that a component has moved, its size has changed, or its visibility has changed.
ContainerEvent	ContainerListener	When a component is added to (or withdrawn from) a container, a container object generates this event.
FocusEvent	FocusListener	These are events connected to attention, such as focus, focusin, focusout, and blur.
ItemEvent	ItemListener	An event that indicates whether or not an item was selected.
KeyEvent	KeyListener	An event that occurs as a result of a series of keystrokes on the keyboard.
MouseEvent	MouseListener & MouseMotionListener	The events that occur as a result of a user’s engagement with the mouse (Pointing Device).
MouseWheelEvent	MouseWheelListener	An event that indicates that the mouse wheel in a component was rotated.
TextEvent	TextListener	An event occurs when the text of an object changes.
WindowEvent	WindowListener	An event that indicates whether a window’s status has changed.

Listener Interface & their methods:

Listener Interface	Methods
ActionListener	actionPerformed()
AdjustmentListener	adjustmentValueChanged()
ComponentListener	componentResized() componentShown() componentMoved() componentHidden()
ContainerListener	componentAdded() componentRemoved()
FocusListener	focusGained() focusLost()
ItemListener	itemStateChanged()
KeyListener	keyTyped() keyPressed() keyReleased()
MouseListener	mousePressed() mouseClicked() mouseEntered() mouseExited() mouseReleased()
MouseMotionListener	mouseMoved() mouseDragged()
MouseWheelListener	mouseWheelMoved()
TextListener	textChanged()
WindowListener	windowActivated() windowDeactivated() windowOpened() windowClosed() windowClosing() windowIconified() windowDeiconified()

Procedure for dealing with events:

• In the class, implement the proper interface.
• Notify the listener about the component.

Note: Example of event handling already seen in the previous post.

Note: also read about the JApplet class in Applet

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