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Bharati Vidyapeeths Institute of Computer Applications and Management, Divya Goel, New Delhi-63 #

Event Handling

Event Handling

Different Mechanism (AWT Introduction) Delegation Event Model

Event Classes

Event Listener Interfaces

Adapter and Inner Classes

Working with windows

Graphics and Text

Learning Objective

Bharati Vidyapeeths Institute of Computer Applications and Management, Divya Goel, New Delhi-63. #

Using AWT Controls

Layout Managers and Menus

Handling Image

Animation Sound and Video

Java AppletBeans

Swings

Servlets

All the various types of AWT events, are

placed in a separate package calledjava.awt.event for the sake of convenience.

The Abstract Window Toolkit (AWT) is

' -

AWT Introduction


windowing, graphics, and user-interface

widget toolkit. The AWT is now part of the

Java Foundation Classes (JFC) The

standard API for providing a graphical user

interface (GUI) for a Java program.

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The AWT provides, among other things:

1. A basic set of GUI widgets such as buttons,text boxes, and menus, etc.

2. The core of the GUI event subsystem .

3. The interface between the native windowin

AWT Introduction


.system and the Java application.

4. Several layout managers.

5. A java.awt.datatransfer package for use withthe Clipboard and Drag and Drop

6.The interface to input devices such as mouse and

keyboards.

7.The AWT Native Interface, which enables rendering

libraries compiled to native code to draw directly to

an AWT Canvas object drawing surface.

AWT Introduction


8. Access to the system tray on supporting systems

9.The ability to launch some desktop applications

such as web browsers and email clients from a

Java application

AWT- It is a package that contains classes, which are used to

create interfaces and in event handling.Java.awt (package)

Component

AWT Definition


Label Button Container Text Component

Window

Frame

Panel

TextField TextArea

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A component is an object that can be

displayed on the screen and can interact with

the user.

It is like a button or scroll bar that has visual

Component Cont.


.

special property like background color and

font color.

Component is an abstract class that

encapsulate all of the attributes of a visual

component.

All user interface elements that are displayed

Component


are subclasses of Component.

A component object is responsible for

remembering the current foreground and

background colors and the currently selected

text font.

Container:- It is a subclass of Component

class. It has additional methods that allowother Component objects to be nested withinit. Other Container objects can be storedinside of a Container (since they are

Container


.various Layout Managers.

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Panel:- It is a concrete subclass of a Container.

It doesnt add any new methods; it simply

implements Container.

Panel is a superclass for Applet.

Panel


,

it is drawn on the surface of a Panel object.

Panel is a window that does not contain a

title bar, Menu bar, or border.

When you run an applet using an applet

viewer, the applet viewer provides the title

and border.

Other components can be added to a panel

Panel Cont.


.

container).

Once these components have been added,

you can position and resize them manually

using the setLocation(), setSize(), or

setBounds() methods defined by Component.

Window:- The window class creates a top-level

window. A top-level window is not contained within

any other object; it sits directly on the

Windows


.

Generally we wont create window objects

directly, instead will use a subclass of

Window called Frame.

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Frame:- sub class of a Window .

It has a title bar, menu bar, borders, and

resizing corners.

When a Frame window is created by a

Frame


program a norma w n ow s crea e ra er

than an applet).

Canvas:- Although it is not part of the hierarchy for

applet or frame window, there is one another type

of window called Canvas.

Canvas encapsulates a blank window upon which

you can draw.

Canvas


ButtonsCommon buttons

Radio buttons

GUI components


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GUI components

Combo boxes

Lists

Menus

GUI components


Spinners

Sliders

GUI components


Textfields

Delegation Event Model

Event model is based on the concept of an

Event Source and Event Listeners. Any object that generates these messages (or

events) is called an Event Source.


. .

event.

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A source must register listeners in order for

the listeners to receive notifications about a

specific type of event. Each type of event has

its own registration method.



are provided by the source that generates

events.

Any object that is interested in receiving

messages (or events ) is called an Event

Listener.

i.e. A listener is an object that is notified



.

It has two major requirements:

1. It must have been registered (add) withone or more sources to receives

notifications about specific types of events.



.

process these notifications.

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According to Sun, the reasons for coming

out with the Java 1.1 Delegation Event

Model are:

1. A source generates an event and sends it



.

2. In this scheme, the listener simply waits

until it receives an event.

3. Once received, the listener processes the

event and then return.

4. The advantage of this design is that the

application logic that processes events is

cleanly separated from the user interface

logic that generates those events.



.

delegate the processing of an event to a

separate piece of code.

6. In this event model, listener must register

with a source in order to receive an eventnotification. This provide an important

benefit: notification are sent only to listeners

that want to receive them.



7. This is a more efficient way to handle events

than the design used by the old java 1.0

approach.

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Old java 1.0 approach:- an event waspropagated up the containment hierarchyuntil it was handled by a component. Thisrequired components to receive events that

they did not process, and it wasted valuable



.

Note: The delegation model eliminates thisoverhead.

8. Facilitate the creation of robust eventhandling code which is less error-prone(strong compile-time checking)

Methods of component class-

1. void setVisible(boolean);

2. void show();

3. void hide();

4. void enable boolean

Methods of component class


.

5. void disable(boolean)

6. void setSize(int w,int height);

7. void setLocation(int left, int top);

8. void setBounds(int left,int top, int w,int h);

9. Add(object of control)

Steps for creating GUI:

Create object of container

Create objects of control

Customize appearance of container and

Steps for creating GUI


contro s

Add controls on container

Show container

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Events: In the delegation model, an event is an

object that describes a state change in a

source.

Some of the activities that cause events to be

Events


,

character via the keyboard, selecting an

item in a list, and clicking the mouse, etc.

Events may also occur that are not directly

caused by interactions with a user interface.

e.g. an event may be generated when a

timer expires, a counter exceeds a value,

Events Cont.


,

an operation is completed, etc.

Event Delegation Model is based on four

concepts:1. The Event Classes

2. The Event Listeners

3. Ex licit Event Enablin

Event Delegation Model is based on four concepts


4. Adapters

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At the root of the java event class hierarchy

is EventObject, which is an java.util.

It is the superclass for all events.

EventObject contains two methods:

Event Delegation Model is based on four concepts


.

getSource()- method returns the source of

the event.

toString()- returns the string equivalent of the

event.

ActionEvent generated by component activation

AdjustmentEvent generated by adjustment of adjustable components

such as scroll bars

ContainerEvent generated when components are added to or removed

from a container

FocusEvent generated when a component receives input

focus

1. Event Class


ItemEvent generated when an item is selected from a list,

choice or check box

KeyEvent generated by keyboard activity

MouseEvent generated by mouse activity

PaintEvent generated when a component is painted

TextEvent generated when a text component is modifiedWindowEvent generated by window activity like minimizing or

maximizing

Listeners for Different Events

For each event type that can occur, theapplication can add event listeners, that have

methods invoked when the event occurs.

2. Event Listener


,

that an actual listener has to implement these

methods.

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The names of the listener classes are simply

derived from the names of the events they

handle,

MouseEvent's have two different types of

2. Event Listener


.

(MouseListener and MouseMotionListener)

Listener- Compare and matches the application

with its event. Every listener in java is an

interface .Hence, need to implement.

Steps:

Event Handling Steps


. .

2. Give body to all the methods of listener

Interfaces.

3. Register the control on which the event isgenerated. (b.addActionlistner(this))

An event listener may be removed from an

Event Source's list of interested Listeners bycalling a remove...Listener() method, passing

in the listener object to be removed.

Event Handling Steps Cont.


, ,

the code below removes the action listener

object listenerObject from the button

m_Button.

m_Button.removeActionListener( listenerObject );

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Any number of event listener objects can

listen for all kinds of events from any number

of event source objects.

e.g. a program might create one listener per

Listeners


single listener for all events from

all sources.

Multiple listeners can register to be notified of

events of a particular type from a particular

source.

Also, the same listener can listen to

Listeners


not cat ons rom erent o ects.

Each type of listeners can be notified only for

its corresponding types of events which canbe generated by specific types of sources.

Listeners


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Many buttons can register the same listener

since all buttons generate the same type of

event. This type of event may be generated

by other types of sources as well.

Multiple sources, single listener


button1

ListItem3

button2

ActionListener

A single source may generate different types

of events and thus register multiple listeners.

Single source, multiple listeners


MouseMotionListener

MouseWheel ListenerMouseWheelEvent

You implement an interface to create a

listener.

In the case of a single source that generates

multiple types of events you can create a

Listeners as interfaces


(remember: a class may extend only one

superclass but implement more than one

interfaces).

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MouseWheel

ListenerMouseWheelEvent

Single source, multiple listeners again


MouseMotion

Listener

MouseWheel +

MouseMotion

Listener

To handle an event you need 3 steps:

Implement the appropriate interface that

will produce your listener class.

Create a listener object.

Event handling steps


Register the listener to the source of

interest.

You register a listener using the

corresponding add function in the form:

component.addSomeListener(listener_object);

You can find the source of an event by using

Putting it into code


e ge ource me o :

event_object.getSource();

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Event Listener MethodActionEvent ActionListener actionPerformed()

AdjustmentEvent AdjustmentListener adjustmentValueChangd()

ComponentEvent ComponentListener componentResized()

componentMoved()

componentShown()

componentHidden()

Listeners for Each Event


FocusEvent FocusListener focusGained()

focusLost()

ItemEvent ItemListener itemStateChanged()

KeyEvent KeyListener keyTyped()

keyPressed()

keyReleased()

MouseEvent MouseListener mouseClicked()

mouseEntered()

mouseExited()

mousePressed()

mouseReleased()

MouseMotionListener

mouseDragged()



mouseMoved()

WindowEvent WindowListener

windowClosed()

windowClosing()

windowDeiconified()

windowIconified()windowOpened()

The following table lists which objects can have whichlistener types added:

GUI Object Listener

Button ActionListener

Choice ItemListener

Listeners for Object


Checkbox ItemListener

Component ComponentListener

FocusListener

KeyListener

MouseListener

MouseMotionListener

Dialog WindowListener

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Frame WindowListener

List ActionListener,ItemListener

MenuItem ActionListener

Scrollbar AdjustmentListener

TextField ActionListener



Note that everyGUI object that inherits from

Component can have Component, Focus, Key,

Mouse and MouseMotion listeners added.

Action events are generated for the following

objects:

GUI Object Action

Button Click on Button

Action Events


st ou e-c c on an tem

MenuItem Click on MenuItem

TextField Press key

Item events are generated for the following objects:

GUI Object ActionChoice Click on item

Checkbox Select an item

Deselect an item

Item Events


List Select an item

Deselect an item

Extend a selection

Reduce a selection

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A subclass can handle its own events by

adding itself as a listener.

In Explicit Event Handling, you control the

order.

3. Listeners vs. Explicit Enabling Event


Java provides adapter classes that

implements the corresponding listener

interface containing more than one method.

The methods in the classes are empty. The

4. Adapter class


Adapter class and override the methods that

you need.

Adapter classes are fully abstract classes

that correspond to listener interfaces.

They are extended (not implemented) and

thus you can ignore methods that do not

Adapter classes Cont.


.

You can use them instead of listeners in the

case that only some of the methods of the

interface are to be used.

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You dont use the abstract specifier and of

course you cannot use multiple inheritance.

Some adapter classes:

KeyAdapter (instead of KeyListener)



ouse apter ouse stener

MouseMotionAdapter

(MouseMotionListener) etc

Event listeners often define many methods.

Since they are interface, you must implement

all of them.

Alternative: Subclass an appropriate adapter



an overr e on y e one you nee .

Adapter Class Listener Interface

ComponentAdapter ComponentListener

Adapter Classes



on a ner ap er on a ner s ener

FocusAdapter FocusListener

KeyAdapter KeyListener

MouseAdapter MouseListener

MouseMotionAdapter MouseMotionListener

WindoAdapter WindowListener

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import java.applet.*;

import java.awt.*;

import java.awt.event.*;

public class MouseAdapterDemo extends

Applet {



public void init() {

setBackground(Color.green);

addMouseListener(newMyMouseAdapter(this));

}}

class MyMouseAdapter extends MouseAdapter {

MouseAdapterDemo mad;

public MyMouseAdapter(MouseAdapterDemo mad){

this.mad = mad;



}

public void mousePressed(MouseEvent me) {

mad.setBackground(Color.red);

mad.repaint();}

public void mouseReleased(MouseEvent me) {

mad.setBackground(Color.green);mad.repaint();

}

}



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There are three methods of event handling:-

1. Outer class

2. Inner class

3. Same class

Methods of event Handling


Notes:: Inner classes also called nested

classes and these are declared within other

classes.

Anonymous Class


program are called anonymous class.

An anonymous class cannot have a

constructor as the class has no name.

You may create all different classes

independently and put them in separate files. you can implement your listeners inside the

class that extends your Frame, making it aninner class.

Inner classes


This enables you to put everything in oneclass (and hence in one file).

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import java.applet.*;import java.awt.*;import java.awt.event.*;/*

Inner Classes


*/public class MouseInnerDemo extendsApplet {



addMouseListener(new MyMouseAdapter());

}

class MyMouseAdapter extends MouseAdapter {

Inner Classes Cont.


public void mousePressed(MouseEvent me) {

setBackground(Color.red);

repaint();}



repaint();} }}

import java.applet.*;import java.awt.*;import java.awt.event.*;/*

*/

public class MouseAnonymousDemo extends Applet {

Anonymous Inner Classes


public void init() {setBackground(Color.green);

addMouseListener(new MouseAdapter() {

public void mousePressed(MouseEvent me) {setBackground(Color.red);repaint();

}

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repaint();

}

Anonymous Inner Classes Cont.


}

}

AnAn Anonymous Inner ClassAnonymous Inner Class

What is the difference between a GUI and a

console app?

From the programmers perspective?

A console app enables interaction through a

Console vs. GUI applications


spec e ow o s.

A GUI app makes it much more flexible. The

user is allowed to perform combinations of

actions.

Class Frame

java.lang.Object

java.awt.Component

Working with Windows


java.awt.Container

java.awt.Window

java.awt.Frame

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A Frame is a top-level window with a title anda border.

The size of the frame includes any areadesignated for the border. The dimensions of

the border area may be obtained using the

Working with Frame Windows Cont.


get nsets met o , owever, s nce t esedimensions are platform-dependent, a validinsets value cannot be obtained until theframe is made displayable by either callingpack or show. Since the border area isincluded in the overall size of the frame, the

border effectively obscures a portion of theframe, constraining the area available forrendering and/or displaying subcomponentsto the rectangle which has an upper-leftcorner location of (insets.left, insets.top), and



- . .by height - (insets.top + insets.bottom).

The default layout for a frame isBorderLayout.

Frame()//creates a standard window that does not contain a title.

Frame(String title) //creates a window withthe title specified by title.Methods

Setting the windows dimension

void setSize(int w,int h);



setVisible(boolean flag)

Setting a window title

void setTitle(String str)

Closing a frame window

setVisible(false)

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Frame:

Frame()-

Frame(String)-

Frame f=new Frame(calculator);


setTitle(String), f.setTitle(Calculator)

getTitle(String)

setLayout(null)

Label -is a control that is used for displaying

messages or output.

1.Label()

2.Label(String)


a e = new a e

l.setText()

l.getText()

TextField- is a control used for single line

input.1. TextField()

2. TextFieldl(String)

Working with Frame Windows


set ext get ext

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Button

Button b=new Button(ok)

Method-

b.setLabel(String)

Working with Frame Windows


b.getLabel(String)

e.g. Button

1.EventName -ActionEvent

getSource()-generate reference of event

object.

Working with Windows


. stener - ct on stener

Method is

public void actionPerformed(ActionEvent e)

3.To Register -addActionListener

java.lang.Object

java.awt.Graphicspublic abstract class Graphics extends Object

The Graphics class is the abstract base class for all graphics

contexts that allow an application to draw onto components

that are realized on various devices, as well as onto off-

Working with Graphics


screen images.

(public class Object

Class Object is the root of the class hierarchy. Every class has

Object as a superclass. All objects, including arrays,

implement the methods of this class.)

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drawLine

public abstract void drawLine(int x1, int y1, int x2,

int y2)

Draws a line, using the current color, between the points

(x1, y1) and (x2, y2) in this graphics context's coordinate

Drawing Lines


.

Parameters:

x1 - the first point's xcoordinate.

y1 - the first point's ycoordinate.

x2 - the second point's xcoordinate.

y2 - the second point's ycoordinate.

import java.awt.*;


public class Lines extends Applet

{

ublic void aint Gra hics

Drawing Lines Example


{

g.drawLine(40,25,250,180);

g.drawLine(75,90,400,400);

}

}

drawRect

public void drawRect(int x, int y, int width, int height) Draws the outline of the specified rectangle. The left and

right edges of the rectangle are at x and x + width. Thetop and bottom edges are at y and y + height. Therectangle is drawn using the graphics context's current

Drawing Rectangles


.

Parameters:

x - the xcoordinate of the rectangle to be drawn.

y - the ycoordinate of the rectangle to be drawn.

width - the width of the rectangle to be drawn.

height - the height of the rectangle to be drawn

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fillRect

public abstract void fillRect(int x, int y, int width, int height)

Fills the specified rectangle. The left and right edges of

the rectangle are at x and x + width - 1. The top and

bottom edges are at y and y + height - 1. The resulting

rectangle covers an area width pixels wide by height

Drawing Rectangles Cont.


pixels tall. The rectangle is filled using the graphics

context's current color.

Parameters:

x - the xcoordinate of the rectangle to be filled.

y - the ycoordinate of the rectangle to be filled.

width - the width of the rectangle to be filled.

height - the height of the rectangle to be filled.

import java.awt.*;



{


Drawing Rectangle Example


{

g.drawRect(10,10,60,50);

g.fillRect(100,10,60,50);

}

}

drawRoundRect

public abstract void drawRoundRect(int x, int y, int width,int height, int arcWidth, int arcHeight) Draws an outlined round-cornered rectangle using this graphics

context's current color. The left and right edges of the rectangle areat x and x + width, respectively. The top and bottom edges of therectangle are at y and y + height.

Drawing Rounded Rectangle


Parameters:

x - the xcoordinate of the rectangle to be drawn.

y - the ycoordinate of the rectangle to be drawn.

width - the width of the rectangle to be drawn.

height - the height of the rectangle to be drawn.

arcWidth - the horizontal diameter of the arc at the four corners.

arcHeight - the vertical diameter of the arc at the four corners.

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fillRoundRect

public abstract void fillRoundRect(int x, int y,int width, int height, int arcWidth, int arcHeight) Fills the specified rounded corner rectangle with the

current color. The left and right edges of the rectangle are

at x and x + width - 1, respectively. The top and bottom

Drawing Rounded Rectangle Cont.


e ges o e rec ang e are a y an y + e g - .

Parameters:

x - the xcoordinate of the rectangle to be filled.

y - the ycoordinate of the rectangle to be filled.

width - the width of the rectangle to be filled.

height - the height of the rectangle to be filled.

import java.awt.*;



{


Drawing Rounded Rectangle Example.


{

g.drawRoundRect(190,10,60,50,15,15);

g.fillRoundRect(70,90,140,100,30,40);

}

}

drawOval

public abstract void drawOval(int x, int y, int width,int height) Draws the outline of an oval. The result is a circle or

ellipse that fits within the rectangle specified by the x, y,width, and height arguments. The oval covers an area

Drawing Oval Example.


a s w + p xe s w e an e g + p x e s a .

Parameters:

x - the xcoordinate of the upper left corner of the oval to bedrawn.

y - the ycoordinate of the upper left corner of the oval to bedrawn.

width - the width of the oval to be drawn.

height - the height of the oval to be drawn.

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fillOval

public abstract void fillOval(int x, int y, int width,int height) Fills an oval bounded by the specified rectangle with the

current color.

Fill Oval Example


Parameters:

x - the xcoordinate of the upper left corner of the oval to befilled.

y - the ycoordinate of the upper left corner of the oval to befilled.

width - the width of the oval to be filled.

height - the height of the oval to be filled.

drawArc

public abstract void drawArc(int x, int y, int width, int height,int startAngle, int arcAngle)

Draws the outline of a circular or elliptical arc coveringthe specified rectangle. The resulting arc begins atstartAngle and extends for arcAngle degrees, using thecurrent color. Angles are interpreted such that 0 degrees

'

Draw Arc Example


.counter-clockwise rotation while a negative valueindicates a clockwise rotation.

The center of the arc is the center of the rectangle whoseorigin is (x, y) and whose size is specified by the widthand height arguments.

The resulting arc covers an area width + 1 pixels wide byheight + 1 pixels tall.

The angles are specified relative to the non-squareextents of the bounding rectangle such that 45 degrees

always falls on the line from the center of the ellipse tothe upper right corner of the bounding rectangle. As aresult, if the bounding rectangle is noticeably longer inone axis than the other, the angles to the start and end ofthe arc segment will be skewed farther along the longeraxis of the bounds.

Draw Arc Example Cont.


Parameters:

x - thexcoordinate of the upper-left corner of the arc to be drawn.

y - the ycoordinate of the upper-left corner of the arc to be drawn.width - the width of the arc to be drawn.

height - the height of the arc to be drawn.

startAngle - the beginning angle.

arcAngle - the angular extent of the arc, relative to the start angle.

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fillArc

public abstract void fillArc(int x, int y, int width, int height,int startAngle, int arcAngle)

Fills a circular or elliptical arc covering the specifiedrectangle. The resulting arc begins at startAngle andextends for arcAngle degrees. Angles are interpreted

such that 0 degrees is at the 3 o'clock position. A positive-

Fill Arc Example Cont.


negative value indicates a clockwise rotation.

The center of the arc is the center of the rectangle whoseorigin is (x, y) and whose size is specified by the widthand height arguments.

The resulting arc covers an area width + 1 pixels wide byheight + 1 pixels tall.

The angles are specified relative to the non-squareextents of the bounding rectangle such that 45 degreesalways falls on the line from the center of the ellipse tothe upper right corner of the bounding rectangle. As aresult, if the bounding rectangle is noticeably longer inone axis than the other, the angles to the start and end ofthe arc segment will be skewed farther along the longeraxis of the bounds.

Fill Arc Example Cont.


Parameters:

x - the xcoordinate of the upper-left corner of the arc to be filled.

y - the ycoordinate of the upper-left corner of the arc to be filled.width - the width of the arc to be filled.

height - the height of the arc to be filled.

startAngle - the beginning angle.

arcAngle - the angular extent of the arc, relative to the start angle.

drawString

public abstract void drawString(String str, int x, int y) Draws the text given by the specified string, using this

graphics context's current font and color. The baseline of

the leftmost character is at position (x, y) in this graphics

'

Draw String Example


.

Parameters:

str - the string to be drawn.

x - the xcoordinate.

y - the ycoordinate.

Etc.

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Text strings

You already met the instruction used todisplay strings on the screen. In case youdidn't, you won't be surprised to hear that it is

drawString. Just to remind you - a string is a

Draw String Example Cont


p ece o text, anyt ng rom a s ng echaracter (a term which includes letters,punctuation, symbols such as @ or ^, andeven the space character) to a wholesentence. Strings are specified by placingthem within double quotation marks.

The method drawString is given three parametersbetween brackets. The first item is the string itselfto be displayed on the screen. The other twonumbers specify where the string is to appear. Itrepresents the top-left corner of the string.However, the second number actually specifies the

Draw String Example Cont


y-co-ordinate of a line on which the text sits. Somecharacters, such as 'g' or 'y' will drop down belowthis imaginary line, as shown in the followingexample:

g.drawString("This is hugely easy",40,60);

If you don't specify a colour for drawing shapes or

text, then Java uses the default colour of black.

Specifying a colour is fairly easy - although you

can only specify one of 13 standard colours

Working with colors


.

There is a standard method built into graphics

environment variables called setColor (note the

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American spelling of 'Color'). It expects to be

given a colour name, but the colour name

must be of a standard type specified in yet

another class called Color. What all this

means is that colours are chosen as follows:

Working with colors Cont.


g.setColor(Color.blue);

g.setColor(Color.orange);

Here are the thirteen standard colours. Make

sure you use them exactly as specified -

don't alter the case of the letters or insert

spaces in the middle of them, and note the

s ellin of 'Gra '.



Black Gray Orange Yellow Blue

Green Pink Cyan lightGray Red

darkGray Magenta white

Any colour that you choose will then be used

for drawing all lines, text, shapes and as thefill-in colour for shapes until you choose

another colour. You can also determine the

colour of the back round to the a let. This



is done using the following instruction:

setBackground(Color.cyan);

Again, like the setColor method, it is

important to note that the name of the

method is all lower case letters except for the

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capital B in the middle. However, please note

that setBackground is not part of the graphics

environment, and as such, does not need to

be preceded by g. In fact, if you do put g. at

the be innin then the Java com iler



,complains. I have fallen into this trap many

times!

repaint

Occasionally, there will be points in theprogram where you will want it redraw thescreen. Perhaps the screen has changed(the paint method can easily cope with if

Working with repaint()


statements t at get t to raw erent t ngsin different circumstances). To call the paintmethod in these circumstances, use thefollowing instruction:

repaint(); Note that there are no parameters

(no numbers, strings or graphicsenvironments) passed to this method, but

you still must include the two brackets and

follow them with the obli ator semicolon,

Working with repaint()0.


like this ();

It is vital that you don't include this method

inside the paint method itself. If you did, the

paint method would never terminate, as it

would always be calling itself.

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Controls are components that allows a user tointeract with your application in various ways- e.g. acommonly used control is the push button.

The AWT supports the following types of controls:

Lables

Push buttons

Using AWT Controls


Check boxes

Choice lists

Lists

Scroll bars

Text editing

These controls are subclass of Component.

Adding and Removing Controls

To include a control in a window, you must add it tothe window by using add() method, which is definedby container.

Using AWT Controls Cont.


Compobj=is an instance of the control that you wantto add.a reference to compobjc is returned.

Once a control has been added it will automatically be

visible whenever its parent window is displayed.void remove(Componenet obj) and removeAll() are

used.// to remove control from a window

Responding to controls

Except for Labels, which are passive controls, all controlsgenerate events when they are accessed by the user.

Labels



.

Label()

Label(String str)

Label(String str, int how)

Where Label.LEFT, Label.RIGHT, Label.CENTER

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Buttons

A push button is a componenet that contains a label

and that generates an event when it is pressed.

These are objects of type Button.

Button()



Button(String str)

Choice and List

Event- ItemEvent

Listener- ItemListener

Method- public void



ItemStateChanged(ItemEvent e)

Register- addItemListener(ItemListener)

Scrollbar (horizontal/vertical)

Event- AdjustmentEvent

Listener- AdjustmentListener

Method- public void



AdjustmentValueChanged(AdjustmentEvent

e)

Register- addAdjustmentListener(ItemListener)

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CheckBox- Multiple Selection

checkBox(String)

e.g. checkBox c=new CheckBox(string);

checkBox(string,Boolean)



e.g. checkBox c1=new CheckBox(study,true);

RadioButton- Single Selection

checkBox(String,Boolean,CheckBoxGroupobject)

e.g. checkBoxGroup cg=new CheckBoxGroup(string);

checkBox c=new CheckBox(Male,true,cg);



e.g. checkBox c1=new CheckBox(Female,false,cg);

You use layout managers to design your GUIs.

There are several managers like:

FlowLayout

BorderLayout

Layout Managers


GridLayout

CardLayout

GridBagLayout

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Default layout

Components laid out from the top-left corner,

from left to right and top to bottom like a text.

FlowLayout


BorderLayout


Places components in up to five areas: top, bottom, left,

right, and center. All extra space is placed in the center

area

GridLayout


Simply makes a bunch of components

equal in size and displays them in the

requested number of rows and columns

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lets you implement an

area that contains

different components at

different times.

A CardLayout is often

controlled by a combo

CardLayout


box, with the state of

the combo box

determining which

panel (group of

components) the

CardLayout displays.

is a sophisticated, flexible layout manager. It

aligns components by placing them within a

grid of cells, allowing some components to

span more than one cell.

GridBagLayout


Putting it into code:

Setting the manager:Container myCont = getContentPane();myCont.setLayout(new FlowLayout());

Layout Managers Code


ng omponen s:

myCont.add(aComponent, BorderLayout.WEST);

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The java.awt.Image class is actually abstract.

However, methods such as getImage(URL)

in the Applet class return an instance of a

concrete subclass provided by the particular

JVM im lementation. The details of that

Handling Image


subclass are not important since you invoke

only methods listed in the Image class, many

of which are overridden by the subclass.

The Image class provides only minimal access toinformation about the image. It does include themethods

int getWidth (ImageObserver)int getHeight (ImageObserver)

that return the dimensions of an ima e.

Handling Image Cont.


You can draw on an image just as you would draw ona component by obtaining the graphics contextobject via the Image class method

Graphics getGraphics ()

You then invoke the usual drawing methods in theGraphics object to draw on the image.

You can create an image just to draw on it using the

createImage() method from the Component classas in the following snippet:

Image image = createImage (width, height);

Handling Image Cont.


Graphics g = image.getGraphics ();

paint (g); // Your paint() method does the usual drawingoperations

// but on the image rather than on a component.

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Threads and Animation

The only functions we have seen in applets so

far are init(), paint(), and functions called in

response to input events. All of these

Animation


of work and return quickly. There has been

no opportunity, so far, for a function to loop

and do some continuous work.

This applet creates a thread, a separate

stream of execution, to perform a

background task. The body of the thread's

code is in the run() function. In this case, the

Animation Cont.


variable i once every 1000 milliseconds, and

cause the applet to redraw itself. The result is

a simple animation.


import java.awt.*;

public class Threads1 extends Applet implementsRunnable {

Animation Cont.


int width, height;

int i = 0;

Thread t = null;

boolean threadSuspended;

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// Executed when the applet is first created.


System.out.println("init(): begin");

width = getSize().width;

height = getSize().height;

setBackground( Color.black );

" "

Animation Cont.


. .

}

// Executed when the applet is destroyed.

public void destroy() {

System.out.println("destroy()");

}

// Executed after the applet is created; and also whenever

// the browser returns to the page containing the applet.

public void start() {

System.out.println("start(): begin");

if ( t == null ) {

System.out.println("start(): creating thread");

=

Animation Cont.


System.out.println("start(): starting thread");

threadSuspended = false;

t.start();

}

else {

if ( threadSuspended ) {threadSuspended = false;

System.out.println("start(): notifying thread");

synchronized( this ) {

Animation Cont.


notify();

}

}

}

System.out.println("start(): end");

}

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// Executed whenever the browser leaves the page containing theapplet.

public void stop() {

System.out.println("stop(): begin");threadSuspended = true;

}

// Executed within the thread that this applet created.

Animation Cont.


public void run() {

System.out.println("run(): begin");

try {

while (true) {

System.out.println("run(): awake");// Here's where the thread does some work

++i; // this is shorthand for "i = i+1;"

if ( i == 10 ) {

i = 0; }showStatus( "i is " + i );

// Now the thread checks to see if it should suspend itself

if ( threadSuspended ) {synchronized( this ) {

while ( threadSuspended ) {

System.out.println("run(): waiting");

wait();

}

}

Animation Cont.


}

System.out.println("run(): requesting repaint");

repaint();

System.out.println("run(): sleeping");t.sleep( 1000 ); // interval given in milliseconds

}}

catch (InterruptedException e) { }

System.out.println("run(): end");}

// Executed whenever the applet is asked to redraw

itself.public void paint( Graphics g ) {

System.out.println("paint()");

g.setColor( Color.green );

Animation Cont.


g.drawLine( width, height, i * width / 10, 0 );

}

}

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The Java Media Framework API (JMF)

enables audio, video and other time-based

media to be added to applications and

applets built on Java technology. This

o tional acka e, which can ca ture,

Sound And Video


playback, stream, and transcode multiple

media formats, extends the Java 2 Platform,

Standard Edition (J2SE) for multimedia

developers by providing a powerful toolkit to

develop scalable, cross-platform technology.

APPLET

An Applet is Loaded into a java-enabledprogram (Netscape, Applet Viewer)

Applet is not a stand-alone program (no mainmethod), structured to run inside anotherprogram (browser)


JVM runs applications, but not applets. Anapplet can run as an application if it defines amain().

Applets are usually event-driven.

Does I/O through a GUI, only displays error

messages with stdout. Applets subclass java.applet

Security - applets barred from reading/writing

APPLET Cont.


, ,

make network connections (except to its

host), cant execute programs, etc...

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Applet lifecycle: (methods overridden from

Applet class):

init(), start(), paint(g),stop(), destroy()

Loading an applet

APPLET Life Cycle


an instance of the applets controlling class

(Applet subclass) created

applet initializes itself

applet starts running

Leaving and returning to applet page

when page is left, applet stops

upon page return, applet starts

Applet reloading/unloading

APPLET Life Cycle Cont.


applet performs finalcleanup, before

reloading

Browser quitting - (applet stops, performs

final cleanup)

Java Bean is a developed by Sun

Microsystems that defines how Java objectsinteract.

An object that conforms to this specificationis called a JavaBean, and is similar to an

Bean


ct ve contro .

It can be used by any application thatunderstands the JavaBeans format.

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The principal difference between ActiveX

controls and JavaBeans are that ActiveX

controls can be developed in any

programming language but executed only on

a Windows latform, whereas JavaBeans

Bean Cont.


can be developed only in Java, but can run

on any platform.

A java bean is a software component that has been

designed to be reusable in a variety of different

environment.

It may perform a simple function , such as checking

the spelling of a document, or a complex function, .

Bean Cont.


A bean may be visible and invisible to end user.

e.g. Button on a GUI..

Software to generate a pie chart from a set of data

points is an example of a Bean that can execute

locally.

Advantage

A software component architecture provides

standard mechanism to deal with softwarebuilding blocks:

A bean obtain all the benefits of javas write-

-


, .

The properties, events, and method of a

Bean that are exposed to an application

builder tool can be controlled.

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Java beans are a framework for creating

components in Java.

AWT and Swing packages are built within

this framework

Java Beans


a e o n w grap c eve opmen

environments such as Jbuilder and Forte.

An extension is Java Enterprise Beans

Code must be written correctly

Access methods must begin with get

Mutation methods must begin with set

Code must support event handling

Bean Rules


Objects must be persistent, i.e. implement

serializable

Introspection used to asses what a bean can

do (which methods it has)

There is also an interface BeanInfo to give

development tools more information

Java Beans: Development Environments


Tools can change a beans properties, e.g.

background color in a window if the window

is regarded as a bean.

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We learned that JavaBeans are Java classes

which adhere to an extremely simple coding

convention. All you have to do is to

implement java.io.Serializable interface, use

a ublic em t ar ument constructor and

Summary


provide public getter and setter methods to

get and set the values of private variables

( properties ).

Swing is a widget toolkit for Java. It is part of

Sun Microsystems' Java Foundation Classes

(JFC) an API for providing a graphical

user interface (GUI) for Java programs.

Swing


sophisticated set of GUI components than

the earlier Abstract Window Toolkit.

The Java Swing provides the multiple

platform independent APIs interfaces forinteracting between the users and GUIscomponents. All Java Swing classes importsform the import javax.swing.*; package. Javaprovides an interactive features for design

Swing Cont.


t e s too t or components e: a e s,buttons, text boxes, checkboxes, comboboxes, panels and sliders etc. All AWTflexible components can be handled by theJava Swing.

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The Java Swing supports the plugging

between the look and feel features. The look

and feel that means the dramatically

changing in the component like JFrame,

JWindow, JDialo etc. for viewin it into the

Swing Cont.


several types of window.

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE)

Above code sets the operation of close operation to

Exit the application using the System exit method.

import javax.swing.*;

public class Swing_Create_Frame{

public static void main(String[] args)

{JFrame frame = new JFrame("Frame in Java Swing");

Creating a frame by usingSwing


. ,

frame.setVisible(true);

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

}

import javax.swing.JFrame;

public class Simple extends JFrame{ public Simple()

{ setSize(300, 200);

setTitle("Simple");

OR Creating a frame by using Swing


se e au ose pera on _ _ ;public static void main(String[] args)

{ Simple simple = new Simple();simple.setVisible(true);

}

}

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Efficient, Convenient, Powerful, Portable, Secure, Inexpensive

Lightweight threads instead of OS threads created

Single copy of code brought into memory for all threads

versus per thread

Servlet

Why Java Servlets Instead of CGI?


Data (session state) can be stored across threads within

servlet container

Java is portable and secure

Requires little expense once servlet container integrated

with web server

The advantages of using servlets is their fastperformance and ease of use combined withmore power over traditional CGI. TraditionalCGI scripts written in Java have a number ofdisadvantages when it comes to

Advantages


.a new process is created for each call of theCGI script. This overhead of process creationcan be very system intensive especially

when the script does relatively fast

operations (process creation will take more

time than CGI script execution). Java servletssolve this problem by allowing each requestto be handled by a separate Java threadwithin the Web server process, omittingseparate process forking by the HTTP

Advantages Cont.


aemon. n a t on, s mu taneousrequest causes the CGI script to be copiedand loaded into memory as many times asthere are requests. However with servletsthere are same amount of threads as requestbut there will only be one copy of the servletclass created in memory.

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Java Servlet Objects on Server Side

Managed by Servlet Container

Loads/unloads servlets

Directs requests to servlets

Servlet Structure


Request doGet()

Each request is run as its own thread

Web App with Servlets

GET

Servlet Cont.


HEADERS

BODY

Servlet

doGet()

Servlet Container

5 Simple Steps for Java Servlets

1. Subclass off HttpServlet

2. Override doGet(....) method

3. HttpServletRequest

Servlet Cont.


getParameter("paramName")

4. HttpServletResponse

set Content Type

get PrintWriter

send text to client via PrintWriter

5. Don't use instance variables

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Servlet Creation

Single instance created

init() method called

You can override init() in your subclass of

Servlet Lifecycle


HttpServlet to do some initial code....

init() is NOT called again on further requests

On each request, the server spawns a new

thread and calls service()

service checks HTTP re uest t e and

Servlet Cycle Cont.

(Service Method)


calls appropriate doXXXX (Get, Post, Put...)

don't override service (unless you really

know what you're doing)

In this chapter, you learnt about Java events

and the delegation event model necessaryto support them. More specifically, youlearned about Java events, including theevent listener capable of generating them

Summary


library. You saw examples of using theswings that are more useful in eventhandling and a Java Servlet is an efficient,convenient, powerful, portable, secure,inexpensive thats why it is more useful.

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Event-driven programming provides the means to

develop flexible applications where the user

determines program flow. Implementing event

handlers in Java is generally straightforward, but it's

important to know which approach is best for which

Conclusion


. ,

most common ways to implement event handling:

dispatching events to an object, using an

anonymous class to dispatch an event directly to

the method that handles it, and using reflection to

write a generic class that dispatches events to the

event handler method.

Objective type Questions

Q1) The CheckboxGroup class is a subclass of the Component

class.

(a)True

(b)False

-

Review Questions


widths wide and 10 characters height tall.what code do you

use?

(a) New TextArea(80,10)

(b) New TextArea(10,80)

Q3)Which of the following are direct or indirect subclasses of

container(a)Frame

(b)TextArea

MenuBar

Review Questions Cont.


(e)Applet

Q4)Which method will cause a frame to be displayed

(a)show()

(b)setVisible()

display()

(d)DisplayFrame()

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Q5)Which method is method to set the layout of a

container

startLayout()

initLayout()

layoutContainer()



setLayout()

Short Questions

Q1)What is the difference between JDBC and ODBC?

Q2)What are the types of JDBC Driver Models and explain

them?-

Q3)What is source and listener?-



-

Q5)What is meant by controls and what are different types of

controls in AWT?-

Q6)What is the difference between choice and list?-

Q7)What is the difference between scrollbar and scrollpane?Q8)What is an event and what are the models available for

event handling?

Long Questions

Q1)What are the steps involved for making a connection with adatabase or how do you connect to a database?

Q2)What is the difference between applications and applets?-

Q3)How are the elements of different layouts organized


over the event-inheritance model?

Q5)What is a layout manager and what are different types of

Documents

unit-3 New