Event Model (in Java 1.1)

event = change of state (state transition) [on UI component]

event ® action when e do S

General Model

JDK 1.1 Event Model (Delegation-based)

When an user action on a component c generates an event e, applications A1 and A2 ask the component object c, representing the user interface component c, to execute S1 and S2, respectively, i.e., the applications delegate the responsibility of executing S1 and S2 to the component c.

There are different types of event objects (event classes in java.awt.event.*) and associated with each event type there are a fixed set of methods, defined by an event listener interface, that can be executed by a component.

Event Class	Listener Interface	Adapter	Listener Methods
ActionEvent	ActionListener		actionPerformed()
AdjustmentEvent	AdjustmentListener		adustmentValueChanged()
ComponentEvent	ComponentListener	ComponentAdapter	componentHidden() componentMoved() componentResized() componentShown()
ContainerEvent	ContainerListener	ContainerAdapter	componentAdded() componentRemoved()
FocusEvent	FocusListener	FocusAdapter	focusGained() focusLost()
ItemEvent	ItemListener		itemStateChanged()
KeyEvent	KeyListener	KeyAdapter	keyPressed() keyReleased() keyTyped()
MouseEvent	MouseListener MouseMotionListener	MouseAdapter MouseMotionAdapter	mouseClicked() mouseEntered() mouseExited() mousePressed() mouseReleased() mouseDragged() mouseMoved()
TextEvent	TextListener		textValueChanged()
WindowEvent	WindowListener	WindowAdapter	windowActivated() windowClosed() windowClosing() windowDeactivated() windowDeiconified() windowIconified() windowOpened()

Event Types, Listnener Methods, and Adapters

[Table 7-6, page 151, 2^nd Edition]

Each component (c) keeps a list of Listener objects (i.e., an object that implements a Listener interface), each of which is owned by an application (A1) and contains the action (method S1) to be executed when the component receives a corresponding event (e).

For each event listener interface with more than one methods, there is an adapter class that implements an empty body for each method in the interface.

Event Model (JDK 1.1)

Component	Events Generated
Button	ActionEvent
Checkbox	ItemEvent
CheckboxMenuItem	ItemEvent
Choice	ItemEvent
Component	ComponentEvent FocusEvent KeyEvent MouseEvent
Container	ContainerEvent
List	ActionEvent ItemEvent
MenuItem	ActionEvent
Scrollbar	AdjustmentEvent
TextComponent	TextEvent
TextField	ActionEvent
Window	WindowEvent

AWT Components and The Events They Generate [Table 7-7, page 152]

WindowEvent e

InOut Example 3

	WindowListener Object (Implements WindowListner Interface)

Event Classes

MouseEvent methods

Object getSource()

Component getComponent()

long getWhen() time-stamp for the event

int getModifiers() keyboard modifier, mouse button

int getClickCount()

Point getPoint()

int getX()

int getY()

ActionEvent methods

String getActionCommand()

A string set by Button or MenuItem method

setActionCommand(String)

InOut Examples

Create a frame of size width (x) = 200

height (y) = 100

Does not terminate, i.e.,

no response to events:

WindowClose

windowOpened windowClosing windowClosed windowIconified windowDeiconified windowActivated windowDeactivated

java.awt =

a package (class library) for Abstract Windowing Toolkit (AWT)

java.awt.*

= all classes in java.awt

import

= make the class names defined java.awt available to the following context

1.

class InOut0 {

public static void main(String[] args) {

java.awt.Frame f = new java.awt.Frame("InOut");

f.resize(200,100);

f.show();

}

}

2.

import java.awt.*;

class InOut0_1 {

public static void main(String[] args) {

Frame f = new Frame("InOut");

f.resize(200,100);

f.show();

}

}

3.

Frame f is a container.

When user clicks the window closing button of f, a windowClosing event is generated by f (i.e., f is the source of the event.)

f, as a component, maintains a list of objects that implements the interface WindowListener.

The InOut1 class creates a new object of an anonymous subclass of WindowAdaptor class, and add it to f’s list of WindowListeners. The anonymous subclass object overriding the WindowAdaptor’s method, windowClosing(), defines the action to be performed on behalf of the InOut1 object, i.e., System.exit().

When a windowClosing event occurs, the frame f executes the windowClosing method of each element of its WindowListener’s list.

[JDK1.1 Event Model]

import java.awt.*;

import java.awt.event.*;

class InOut1 {

public static void main(String[] args) {

Frame f = new Frame("InOut");

f.resize(200,100);

f.show();

f.addWindowListener(new WindowAdapter(){

public void windowClosing(WindowEvent e) {

System.exit(0);

}

});

}

}

/* do nothing, but exit by window close */

package java.awt.event;

import java.util.EventListener;

public interface WindowListener extends EventListener {

public void windowOpened(WindowEvent e);

public void windowClosing(WindowEvent e);

public void windowClosed(WindowEvent e);

public void windowIconified(WindowEvent e);

public void windowDeiconified(WindowEvent e);

public void windowActivated(WindowEvent e);

public void windowDeactivated(WindowEvent e);

}

package java.awt.event;

public abstract class WindowAdapter implements WindowListener {

public void windowOpened(WindowEvent e) {}

public void windowClosing(WindowEvent e) {}

public void windowClosed(WindowEvent e) {}

public void windowIconified(WindowEvent e) {}

public void windowDeiconified(WindowEvent e) {}

public void windowActivated(WindowEvent e) {}

public void windowDeactivated(WindowEvent e) {}

}

import java.awt.*;

import java.awt.event.*;

class InOut1 {

public static void main(String[] args) {

Frame f = new Frame("InOut");

f.resize(200,100);

f.show();

f.addWindowListener(new WindowAdapter(){

public void windowClosing(WindowEvent e) {

System.exit(0);

}

});

}

}

/* do nothing, but exit by window close */

InOut Example 3

	WindowListener Object