AWT by Kamalakar Dandu

8/2/2019 AWT by Kamalakar Dandu

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Java Graphics Programming


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Using AWT Components

Figure shows the inheritance hierarchies for

all the AWT component classes.


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The AWT

Provides basic GUI components which areused in all Java applets and applications

Has super classes which can be extendedand their properties inherited; classes can

also be abstract Ensures that every GUI component that isdisplayed on the screen is a subclass of theabstract class Component

Contains Container which is an abstractsubclass of Component and which includestwo subclasses

Panel

Window


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Containers

The two main types of containers are Windowand Panel.

Windows are objects ofjava.awt.Window.

Panels are objects of java.awt.Panel.


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Building Graphical User

Interfaces

The position and size of a component in a container

is determined by a layout manager. You can control the size or position of components

by disabling the layout manager.

You must Then use setLocation(),

setSize(), or setBounds() on components tolocate them in the container.


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Frames

Are subclasses of Window

Have title and resize corners

Inherit from Component and add components withthe addmethod

Can be used to create invisible Frame objectswith a title specified by String

Have Border Layout as the default layoutManager

Use the setLayout method to change the

default layout manager


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Panels

Provide a space for components

Allow subpanels to have their own layout

manager Add components with the add method


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Container Layouts

Flow Layout - Default layout for a Paneland Applet.

Border Layout - Default layout for aFrame

Grid Layout

Card Layout

GridBag Layout


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The Frame class provides windows for applets and applications.

Every GUI application needs at least one Frame.

How to use Frames :


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How to use Frames :

Import java.awt.*;

public class MyWindow extends Frame {

MyWindow() {

setTitle(Employee Registration Form);

setSize(200,200);

setVisible(true);

}

public static void main(String[] ar) {

MyWindow mw = new MyWindow();

}

}


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Here's an example of using a Panel instance to hold someComponents:

Panel p1 = new Panel();

p1.add(new Button(Submit"));

p1.add(new Button(Reset"));p1.add(new Button(Cancel"));

add(North,p1);//adding to North

// side of the Frame

How to use Panels:


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The Button class provides a default button implementation.A button is a simple control that generates an action event

when the user clicks it.

//In initialization code:

Buttonb1 = new Button();

b1.setLabel(Click Me");

How to use Buttons :


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TheLabel class provides an easy way of putting unselectable

text in your program's GUI.

Labels are aligned to the left of their drawing area, by default.

You can specify that they be centered or right-aligned by

specifying Label.CENTER or Label.RIGHT either to the Label

constructor or to the setAlignment() method. As with

every Component, you can also specify the font and color of a

Label.

How to use Labels :


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Below is the code that the applet uses to create its labels and

set their alignment.

How to use Labels :

Label label1 = new Label();

label1.setText("Left");

Label label2 = new Label("Center");

label2.setAlignment(Label.CENTER);Label label3 = new Label("Right", Label.RIGHT);

Besides the constructor, setText(), andgetAlignment() methods

used above, the Label class also provides getText() andgetAlignment() methods.


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How to use Text Fields :

import java.awt.*;

class TextDemo extends Frame {

TextField tf1, tf2;

TextDemo() {

setLayout(new FlowLayout());

setSize(300, 200);

tf1 = new TextField();tf2 = new TextField();

add(tf1);

add(tf2);

}public static void main(String args[]) {

TextDemo window = new TextDemo();

window.show();

}

}


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Lab Session

Write a program to create a Frame. Create two panels, one

with two buttonsOk and Cancel, using FlowLayout,

and another panel with two text fields one below the other,

using BorderLayout.

Place one panel to the north and one to the south of the

Frame

Write a program to place six text fields in 2 rows by 3

columns fashion.


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Event Driven Programming


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What Is An Event?

Events - Objects that describe what happened

Event source - The generator of an event Event handlers - A method that receives an

event

object,deciphers it,and processes the usersinteraction


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Delegation Model (JDK 1.1

and Beyond )

Events are not accidentally handled.

There is better distribution of work amongthe classes.


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GraphicsThe Color class

Color(int red, int green, int blue) or Color.blue value

setForeground(Color.blue) or setBackground(Color.blue)

The Font class

Font(String name, int style, int size)

Styles - Font.PLAIN, Font.BOLD, Font.ITALIC

can have Font.BOLD | Font.ITALIC also

The FontMetrics class FontMetrics(Font f)

The Graphics class -Every component has a graphics context

Component.getGraphics() - Ex. button.getGraphics();

g.getFontMetrics()


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Lab Session

Write a program to display the name of your company with a

font size of 30, color - black and background - gray in a

frame.

Write a program to display all possible shapes available in

the graphics class, in a frame using the API.


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Creating User Interfaces


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Checkbox

CheckboxGroup

Choice Dialog

List

Menu

TextArea

List of AWT Components


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The Checkbox class provides checkboxes :-

Two-state buttons that can be either "on" or "off".

When the user clicks a checkbox, the checkbox state

changes and generates an event.

If you want a group of checkboxes in which only one

checkbox at a time can be "on", you can add a

CheckboxGroup (You might know this UI element as aradio button.)

How to use Checkboxes :


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Checkbox cb1, cb2, cb3;//These are independent checkboxes.

cb1 = new Checkbox();//Default state is "off" (false).

cb1.setLabel(Java");

cb2 = new Checkbox(Cobol");

cb3 = new Checkbox(Visual Basic");

cb3.setState(true);//Set state to "on" (true).. . .

How to use Checkboxes :

H t Ch i


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A Choice is a Drop Down Menu When the user chooses an item,

the Choice generates an event.

Choices are useful when you need to display a number of

alternatives in a limited amount of space

How to use Choice :


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Choice choice; //Drop Down list of choices

//...Where initialization occurs:

choice = new Choice();choice.addItem(Java");

choice.addItem(Oracle");

choice.addItem(Visual Basic);

choice.addItem(SmallTalk");

How to use Choice :


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How to use Dialogs :

Windows that are dependent on other windows -- with the Dialog

class. - new Dialog(frame), where frame is the parent window.

We can create a dialog with a model using a different constructor.

By default, dialogs are non-modal -- the user can keep them up

and still work in other windows of the application

How to use Dialogs


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How to use Dialogs :

Here's just the code that implements the Dialog object:

public class MyWindow extends Frame {Dialog d;

Label l;

MyWindow() {

d=new Dialog(this,true);

l=new Label(Invalid number entered);

d.add(Center,l);

d.setSize(100,200); //This is a must

d.show(); //To show the dialog window.

// We can activate a dialog window based on

// an event.

}

}


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TheListclass provides a scrollable area containing selectable text

items (one per line).

Lists can allow either multiple selections or just one selection at a

time.

How to use Lists :


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//Build first list, which allows multiple selections.

List1 = new List(2, true);//prefer 2 items visible

List1.add(Unix");

List1.add(Dos");

//Build second list, which allows one selection at a time.

List2 = new List();//Defaults to none visible, only one selectableList2.add(Unix");

List2.add(Dos");

How to use Lists :


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How to use Menus:

Menu classes inherit from theMenuComponent class :

The AWT provides the following MenuComponent subclasses tosupport menus:

MenuBar :

MenuBar represents the platform-dependent notion of agroup of menus attached to a window. MenuBars can notbe

bound to Panels.

Menu :Each menu is represented by a Menu object.

MenuItem :

Each item in a menu is represented by a MenuItem object.


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How to use Menus:

.Here's just the code that deals with menus:

public class MenuWindow extends Frame {public MenuWindow() {

MenuBar mb;

Menu file, edit;

MenuItem newfile, open, close;MenuItem cut, copy, paste;

//Build the menu bar.

mb = new MenuBar();

setMenuBar(mb);//Set menu bar for the frame

Contd. In Next Page...

How to use Menus:


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file= new Menu(File);

mb.add(file);

newfile = new MenuItem(New"); file.add(newfile);

open = new MenuItem(Open"); file.add(open);close = new MenuItem(Close"); file.add(close);

How to use Menus:


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TextArea textArea;

//create text area of 5 rows and 30

//columnstextArea=new TextArea(5,30)

textArea.setEditable(false);

How to use TextArea :


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Lab Session

Write a program to show the appearance of a Notepad program

using all the menu options.

Create a GUI form using all the GUI components covered in

this session.

Write a program to display a Dialog box with a message, usinga Font and a Color class.


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Using Listener Interfaces

Component

Button

Listener

ActionListener

actionPerformed(ActionEvent e) {

}

Event Object

ActionEvent


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List of Listeners

Listener Interfaces Methods

ActionListener void actionPerformed(ActionEvent)

AdjustmentListener adjustmentValueChanged(AdjustmentEvent)

AWTEventListener eventDispatched(AWTEvent)

ComponentListener componentHidden(ComponentEvent)componentMoved(ComponentEvent)

componentResized(ComponentEvent)

componentShown(ComponentEvent)

ContainerListener componentAdded(ContainerEvent)componentRemoved(ContainerEvent)

FocusListener focusGained(FocusEvent)

focusLost(FocusEvent)

ItemListener itemStateChanged(ItemEvent)


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KeyListener keyPressed(KeyEvent)

keyReleased(KeyEvent)

keyTyped(KeyEvent)

MouseListener mouseClicked(MouseEvent)

mouseEntered(MouseEvent)mouseExited(MouseEvent)

mousePressed(MouseEvent)

mouseReleased(MouseEvent)

MouseMotionListener mouseDragged(MouseEvent)

mouseMoved(MouseEvent)

TextListener textValueChanged(TextEvent)


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WindowListener windowActivated(WindowEvent)

windowClosed(WindowEvent)

windowClosing(WindowEvent)

windowDeactivated(WindowEvent)windowDeiconified(WindowEvent)

windowIconified(WindowEvent)

windowOpened(WindowEvent)


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Event Component

ActionEvent Button, List (Double click), Menu

ItemEvent Check box, List, ChoiceKeyEvent Keyboard

MouseEvent Mouse operations

TextEvent TextField and TextArea.

WindowEvent Window, Frame, Dialog


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Multiple Listeners

One component can register itself for more thanone listener.

All registered listeners have their handler called

when the event occurs.


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Lab Session

Write a program to show the event handling of a list, choice,

check box and radio buttons. Show proper messages.

Write a program to change the background color of the frameusing a list of colors.

Create a form with three text fields for Name, Age and Salary.

Show the details on the screen as a single line, when clicked

on the Submit button. Clear the form for next entry.


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Applets


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What is an Applet ?

A Java class that can be embedded within an HTML

page and is downloaded and executed by a web browser.

Is loaded as follows :

Browser loads URL

Browser loads the HTML document

Browser loads applet classes

Browser runs the applet


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Applet Security Restrictions

Most browsers prevent the following

Runtime execution of another program

Any file I/O (input/output)

Calls to any native methods

Attempts to open a socket to any system except the

host that provided the applet.


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Key Applet Methods

init()

start()

stop()

destroy()

paint()


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Applet DisplayApplets are graphical in nature

paint() method is called by the browser environment

Example of an applet that uses a paint() method :

import java.awt.*;import java.applet.*;

public class HelloJava extends Applet {

public void paint(Graphics g) {

g.drawString(Hello Java!,25,25);

}

}


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Applet methods and the Applet LifeCycle

init()

Called when the applet is created

Can be used to initialize data values

start()

Runs when the applet becomes visible

stop()

Called when the applet becomes invisible

destroy()

Called when the browser or the appletviewer is closed

paint()

Called automatically when the applet is started


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AWT Painting

paint(Graphics g)

repaint()

update(Graphics g)


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AWT thread (waiting)

update()

update background

call paint()

paint()

Exposurerepaint()


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What is the appletviewer ?

A Java application that enables you to run applets without

using a web browser

It loads the HTML file supplied as an argument appletviewer HelloJava.html

It needs at least the following HTML code :


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Syntax of applet tag

[ ]

[ ]


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Additional Applet Facilities

getDocumentBase() - Returns a URL object that describes

directory of the current browser page.

getCodeBase() - Returns a URL object that describes the

source directory of the applet class.

getImage(URLbase, Stringtarget) and

getAudioClip(URLbase, Stringtarget) - Use the URL

object as a starting point.


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A sample image test

//HelloJava extended to draw an image

//Assume existence of javalogo.gif

import java.awt.*;

import java.applet.*;

public class HwImage extends Applet {

Image logo;

public void init() {

logo = getImage(getDocumentBase(),

javalogo.gif);}

public void paint(Graphics g) {

g.drawImage(logo,25,25,this);

}

}


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Looping an Audio Clip

Loading an audio clip

Playing an audio clip

Stopping an audio clip


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A sample Audio Looping Test

//HelloJava extended to loop an audio track

//Assume existence of spacemusic.auimport java.awt.Graphics;

import java.applet.*;

public class HwLoop extends Applet {

AudioClip sound;

public void init() {sound=getAudioClip(getDocumentBase(),

spacemusic.au);

}

public void paint(Graphics g) {g.drawString(Audio test,25,25);

}

public void start() { sound.loop(); }

public void stop() { sound.stop(); }

}


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Lab Session

Write a program that demonstrates the use of the life cycle

methods of an applet. Show proper messages on the screen.

Write an applet to load an image file

Write an applet to accept two numbers in text fields and

compute the sum of the numbers when clicked on the Addbutton.


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Advanced Graphics


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Grid Bag Layout Manager

GridBagLayout enables finer control over the size and

placement of individual cells in a grid layout. Each

grid area or component is associated with a particular

GridBagConstraints instance that specifies how the

component is laid out within the display area.

Like GridLayout, the GridBagLayout layout manager

aligns components within a rectangular grid of cells.

Where GridLayout and GridBagLayout differ is in

that GridBagLayout use an object called

GridBagConstraints.


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By setting values within the GridBagConstraints object,

components can be aligned vertically or horizontally (with or

without insets and padding), told to expand to fill the given area

, and instructed on how to behave upon resizing of the window.

You initialize and utilize a GridBagLaoyout and its associated

GriBagConstraints object as follows:private GridBagLayout guiLayout;

private GridBagConstraints guiConstraints;

guiLayout = new GridBagLayout();setLayout(guiLayout);

guiConstraints = new GridBagConstraints();

guiConstraints.anchor = GridBagConstraints.CENTER;


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Using GridBagConstriants

Only new about the code in the previous page is the final

statement:

guiConstraints.anchor = GridBagConstraints.CENTER;

The GridBagConstraints object, associated with the

GridBagLayout layout manager, contains instance variables that

can be set to govern how components are laid out. This instancevariable is used to instruct GridBagLayout on how to place a

component when it is smaller than its cell. Valid values are:

GridBagConstraints.CENTER

GridBagConstraints.NORTH

GridBagConstraints.EAST

GridBagConstraints.SOUTH

GridBagConstraints.SOUTHEAST


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GridBagConstraints Instance Variables

The API pages for GridBagLayout explains the instance variables

used for governing component layout. These are gridx and gridy

These variables specify the characteristics of the cell at the

upper left of the components display area, where the upper left-

most cell has the address gridx=0, gridy=0. gridwidth and gridheight

These variables specify the number of cells in a row

(gridwidth) or column (gridheight) in the components display

area. The default value is 1.

fillfillis used when the components display area is larger than

the components requested size;fill determines whether (and how)

to resize the component.

Contd In Next Page...


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ipadx and ipady

These variables specify the internal padding; that is , howmuch to add to the minimum size of the component.

insets

insets specifies the external padding of the component;

that is, the minimum amount of the space between the

component and the edges of its display area.

anchor

This variable is used when the component is smaller thanits display area; anchordetermines where to the place the

component.


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GridBagConstraints Example

import java.awt.*;

public class GridBagLayoutDemo extends Frame {void makeButton(String name, GridBagConstraints gbc) {

Button button = new Button(name);

add(button, gbc);

}

public GridBagLayoutDemo() {setLayout(new GridBagLayout());

GridBagConstraints c = new GridBagConstraints();

setFont(new Font("Helvetica", Font.PLAIN, 14));

c.fill = GridBagConstraints.BOTH;c.weightx = 1.0;

makeButton("Button1", c);


makeButton("Button3", c); Contd. In Next Page..


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c.gridwidth = GridBagConstraints.REMAINDER;//end row

makeButton("Button4", c);c.weightx = 0.0; //reset to the default

makeButton("Button5", c);//another row

//next-to-last in row

c.gridwidth = GridBagConstraints.RELATIVE;


c.gridwidth = GridBagConstraints.REMAINDER;

//end row


c.gridwidth = 1; //reset to the defaultc.gridheight = 2;

c.weighty = 1.0;


Contd. In Next Page..


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c.weighty = 0.0; //reset to the default

c.gridwidth = GridBagConstraints.REMAINDER;//end row

c.gridheight = 1; //reset to the default



}public static void main(String args[]) {

GridBagLayoutDemo window = new GridBagLayoutDemo();

window.pack();

window.show();}

}


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Card Layout- Create a panel for card layout

- Create different panels as cards and add to this card panel

- Change the card (panel) on some event

Example :

Panel cards;

Panel p1, p2 //for buttons, text fields ....

cards.setLayout(new CardLayout());

cards.add(ButtonPanel,p1);cards.add(TextPanel,p2);

CardLayout cl = (CardLayout) (cards.getLayout());

cl.show(cards, ButtonPanel);


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Lab Session

Write a program to create the login screen using Grid bag

layout.

Exercise (contd )


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Exercise (contd)

16. A need to persist the data has now arisen asthe client observes that the development team iseither getting the data from the console or is

having it stored as string attributes in theprograms. The client wishes that the data shouldbe persisted and reused by any other programs,as well. Hence, store the data in the Collection

into a file. Implement methods to read/write thedata to/from the given file. The access methodsshould be synchronized

Documents

AWT by Kamalakar Dandu