2 event driven programming

5/24/2018 2 Event Driven Programming

1/28

Event-Driven Programming


2/28

Procedural vs. Event-DrivenProgramming

Procedural programming is executed in procedural order

procedural - of or relating to procedure

procedure - a series of steps followed in a regular definite

order

In event-driven programming, code is executed uponactivation of events

e.g. menu buttons can be selected in any order

2


3/28

Taste of Event-DrivenProgramming

The example displays three buttons in the frame.

The content pane's background colour changes when abutton is clicked.

3

ButtonTest


4/28

Events

An event can be defined as a type of signal to theprogram that something has happened

The event is generated by external user actions such as

mouse movements, mouse clicks, and keystrokes, or bythe operating system, such as a timer

4

ColorActionActionListener

JButton

actionPerformed


5/28

The Delegation Model

5

source: SourceClass

+addXListener(listener:XListener)

listener: ListenerClass

User

Action

Trigger an event

XListener

+handler(event: XEvent)

Register by invoking

source.addXListener(listener);(a) A generic source component

with a generic listener

source: JButton

+addActionListener(listener: ActionListener)

listener: CustomListenerClass

ActionListener

+actionPerformed(event: ActionEvent)

Register by invoking

source.addActionListener(listener);(b) A JButton source component

with an ActionListener


6/28

Internal Function of a SourceComponent

6

source: SourceClass

+addXListener(XListener listener)

(a) Internal function of a generic source object

event:XEvent listener1listener2listenern

Keep it a list

Invokelistener1.handler(event)

listener2.handler(event)

listenern.handler(event)

An event istriggered

source: JButton

+addActionListener(ActionListener listener)

(b) Internal function of a JButton object

event:

ctionEvent

listener1listener2listenern

Keep it a list

Invokelistener1.actionPerformed(event)

listener2.actionPerformed(event)

listenern.actionPerformed(event)

An event istriggered


7/28

The Delegation Model: Example

7

JButton okButton = new JButton("OK");

ActionListener listener = new OKListener();

okButton.addActionListener(listener);


8/28

Event Classes

8

AWTEventEventObject

AdjustmentEvent

ComponentEvent

TextEvent

ItemEvent

ActionEvent

InputEvent

WindowEvent

Mouse

KeyEv

ContainerEvent

FocusEvent

PaintEvent

ListSelectionEvent


9/28

Event Information

An event object contains whatever properties whichpertain to the event

You can identify the source object of the event using

the getSource() instance method in the EventObjectclass

The subclasses of EventObject deal with special types ofevents, such as button actions, window events,

component events, mouse movements, and keystrokes

9


10/28

Selected User ActionsUser Action Source Event Generated

Click a button JButton ActionEvent

Click a check box JCheckBox ItemEvent, ActionEvent

Click a radio button JRadioButton ItemEvent, ActionEventPress return on a text field JTextField ActionEvent

Window opened, closed, etc Window WindowEvent

Mouse pressed, released, etc. Component MouseEvent

Key released, pressed, etc. Component KeyEvent

10


11/28

Selected Event HandlersEvent Class Listener Interface Handlers

ActionEvent ActionListener actionPerformed(ActionEvent)

ItemEvent ItemListener itemStateChanged(ItemEvent)

WindowEvent WindowListener windowClosing(WindowEvent)windowOpened(WindowEvent)

windowIconified(WindowEvent)windowDeiconified(WindowEvent)windowClosed(WindowEvent)windowActivated(WindowEvent)windowDeactivated(WindowEvent)

ContainerEvent ContainerListener componentAdded(ContainerEvent)componentRemoved(ContainerEvent)

MouseEvent MouseListener mousePressed(MouseEvent)mouseReleased(MouseEvent)mouseClicked(MouseEvent)mouseEntered(MouseEvent)mouseExited(MouseEvent)

KeyEvent KeyListener keyPressed(KeyEvent)keyReleased(KeyEvent)keyTypeed(KeyEvent)

11


12/28

Inner Class Listeners

A listener class is designed specifically to create alistener object for a GUI component (e.g., a button)

It will not be shared by other applications.

So, it is appropriate to define the listener class inside theframe class as an inner class

12


13/28

Inner Classes

Inner class: A class is a member of another class.

Advantages: In some applications, you can use an innerclass to make programs simple.

An inner class can reference the data and methodsdefined in the outer class in which it nests, so you donot need to pass the reference of the outer class to theconstructor of the inner class.

13


14/28

Inner Classes (cont.)

Inner classes can make programs simple and concise.

An inner class supports the work of its containing outerclass and is compiled into a class named

OuterClassName$InnerClassName.class. For example,the inner class InnerClass in OuterClass is compiled intoOuterClass$InnerClass.class.

14


15/28

Inner Classes (cont.)

An inner class can be declared public, protected, orprivate subject to the same visibility rules applied to amember of the class

An inner class can be declared static A static inner class can be accessed using the outer class

name

A static inner class cannot access nonstatic members of theouter class

15


16/28

Anonymous Inner Classes Anonymous class is declared and initialized simultaneously.

As anonymous class has no name, it can be used only once.

An anonymous inner class must always extend a superclass orimplement an interface, but it cannot have an explicitextends or implements clause.

An anonymous inner class must implement all the abstractmethods in the superclassor in the interface.

An anonymous inner class always uses the no-arg constructorfrom its superclass to create an instance. If an anonymousinner class implements an interface, the constructor isObject().

An anonymous inner class is compiled into a class namedOuterClassName$n.class. For example, if the outer class Testhas two anonymous inner classes, these two classes arecompiled into Test$1.class and Test$2.class.

16


17/28

Anonymous Inner Classes cont.. You use them in situations where you need to create a class

for a specific purpose inside another function, e.g., as a

listener, as a runnable (to spawn a thread), etc.

The idea is that you call them from inside the code of afunction so you never refer to them elsewhere, so youdon't need to name them. The compiler just enumeratesthem.

They are essentially syntactic sugar, and should generally bemoved elsewhere as they grow bigger

We can just instantiate an anonymous inner class without

actually making a separate class.

Use this technique for "quick and dirty" tasks where making anentire class feels unnecessary. Having multiple anonymousinner classes that do exactly the same thing should berefactored to an actual class, be it an inner class or aseparate class.


18/28

Demo Using Anonymous Inner Classes18

PlafTest


19/28

Example: Handling Window Events

Any subclass of the Window class can generate the followingwindow events: window opened, closing, closed, activated,deactivated, iconified, and deiconified.

This program creates a frame, listens to the window events, anddisplays a message to indicate the occurring event.

19

TestWindowEvent


20/28

Using Adapters

To reduce the number of unimplemented listener interfacemethods, you can make use of an adapter instead

The easiest way to use an adapter is to use an anonymousinner class

import java.awt.event.WindowAdapter;...addWindowListener(new WindowAdapter() {public void windowClosing() {System.exit(0);});

The WindowAdapter class implements all of the

WindowListener methods

20


21/28

MouseEvent

21

java.awt.event.MouseEvent

+getButton(): int

+getClickCount(): int+getPoint(): java.awt.Point

+getX(): int

+getY(): int

Indicates which mouse button has been clicked.

Returns the number of mouse clicks associated with this event.Returns a Point object containing the x and y coordinates.

Returns the x-coordinate of the mouse point.

Returns the y-coordinate of the mouse point.

java.awt.event.InputEvent

+getWhen(): long

+isAltDown(): boolean

+isControlDown(): boolean

+isMetaDown(): boolean

+isShiftDown(): boolean

Returns the timestamp when this event occurred.

Returns whether or not the Alt modifier is down on this event.

Returns whether or not the Control modifier is down on this event.

Returns whether or not the Meta modifier is down on this event

Returns whether or not the Shift modifier is down on this event.


22/28

Handling Mouse Events

Java provides two listener interfaces, MouseListener andMouseMotionListener, to handle mouse events.

The MouseListenerlistens for actions such as when the mouse ispressed, released, entered, exited, or clicked.

The MouseMotionListenerlistens for actions such as dragging ormoving the mouse.

22


23/28

Handling Mouse Events

23

java.awt.event.MouseListener

+mousePressed(e: MouseEvent): void

+mouseReleased(e: MouseEvent): void

+mouseClicked(e: MouseEvent): void

+mouseEntered(e: MouseEvent): void

+mouseExited(e: MouseEvent): void

Invoked when the mouse button has been pressed on the

source component.

Invoked when the mouse button has been released on the

source component.Invoked when the mouse button has been clicked (pressed and

released) on the source component.

Invoked when the mouse enters the source component.

Invoked when the mouse exits the source component.

java.awt.event.MouseMotionListener

+mouseDragged(e: MouseEvent): void

+mouseMoved(e: MouseEvent): void

Invoked when a mouse button is moved with a button pressed.

Invoked when a mouse button is moved without a button

pressed.


24/28

Example: Moving Message UsingMouse

24

MoveMessageDemo


25/28

Example: Handling Complex MouseEvents

25

ScribbleDemo


26/28

Handling Keyboard Events

To process a keyboard event, use the following handlersin the KeyListener interface:

keyPressed(KeyEvent e)

Called when a key is pressed. keyReleased(KeyEvent e)

Called when a key is released.

keyTyped(KeyEvent e)

Called when a key is pressed and then

released.

26


27/28

The KeyEvent Class

Methods:

getKeyChar() method

getKeyCode() method

Keys:

Home VK_HOME

End VK_END

Page Up VK_PGUP

Page Down VK_PGDN

etc...

27


28/28

Example: Keyboard EventsDemo

28

KeyEventDemo

2 event driven programming

Documents