session3 - awt

8/4/2019 Session3 - AWT

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Abstract Windowing Toolkit

Session 3


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Abstract Windowing Toolkit / 2 of 29

Objectives

Discuss Containers and Components

Frame Panel

Label

TextFields and TextAreas

Checkboxes and RadioButtons

Choice

Identify events generated by components

Create a standalone AWT application

Describe Abstract Windowing Toolkit (AWT)


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Introduction

These make the language richer in terms of creatinggraphical objects that can be controlled by thedeveloper as well as the user.

One of the most important outcomes of this is thatlanguages have happened to be GUI based.

In this session we discuss how Java supports GUIfeatures and how they are implemented.

As on date, software applications have become user-friendlier because of introducing graphics in user

interfaces


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Abstract Windowing Toolkit

Abstract Windowing Toolkit (AWT) is a setof Java classes that allow us to create a GUI

AWT provides items which enable creation ofan attractive and efficient GUI

Graphical User Interface (GUI) is used to

accept input through a keyboard or a mouse


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Containers

It can be drawn or painted Container class in the java.awt package

directly or indirectly derives two commonlyused containers Frame and Panel

Frame is a separate window and has borders

Panel is an area without borders and iscontained within a window

An area that can hold elements


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Containers - Frame

Can be a component or a container

Can be created using constructors

Some of these constructors are: Frame()

Creates a Frame which is invisible

Frame(String Title)

Creates an invisible Frame with given title

A window that is independent of an applet

and of the browser


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Example

Output



Containers - Panel

Simplest way to create a panel is through itsconstructor Panel( )

A panel has to be added to a frame The frame will be visible only when the two

methods setSize( ) and setVisible( ) are set

Used to group a number of components

together



Example

Output



Component

Examples include textfields, labels,checkboxes, textareas etc.

Some advanced components includescrollbars, scrollpanes and dialogs

Anything that can be placed on a user

interface and can be made visible or resized



Hierarchy of classes in JavaComponent

Button Checkbox Container Choice Canvas

TextComponent

Label

Panel Window

Applet Frame Dialog

TextArea TextField



Various components

Label Text field

Checkbox

Radio button

Button

Text Area



Label

Not user-editable

Can be created using one of the following constructors: Label( )

Creates an empty label

Label(String labeltext)

Creates a label with a given text

Label(String labeltext, int alignment)Creates a label with given alignment where alignment

can be Label.LEFT, Label.RIGHT or Label.CENTER

Generally used to indicate the purpose of an item



Textfield

Generally accepts one line of input

Can be created using one of the following constructors: Textfield()

Creates a new textfield

Textfield(int columns)Creates a new textfield with given number of columns

Textfield(String s)Creates a new textfield with the given string

Textfield(String s, int columns)Creates a new textfield with given string and given

number of columns

GUI element used to input text


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Example

Output


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TextArea

Includes a scrollbar

TextArea can be created using some of the followingconstructors given below: TextArea( )

Creates a new TextArea

TextArea(int rows, int cols)

Creates a new TextArea with given number of rows andcolumns

TextArea(String text, int rows, int cols)Creates a new TextArea with given string, given number

of rows and columns

Used when text is to be accepted has two or more lines


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Example

Output


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Button

The easiest way to trap user action Can create buttons in Java using any of the

following constructors

Button()

Creates a new Button.

Button(String text)

Creates a new Button with the given String

Part of GUI


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Example

Output


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Checkbox

Checkboxes in Java can be created usingconstructors.

Some of these constructors are: Checkbox()

Creates an empty textbox

Checkbox(String text)Creates a checkbox with given string as label

Used for multi-option user input that the usermay select or deselect by clicking them.


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Example

Output


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Radiobuttons

Only one button in a radiobutton group can

be selected. First create a CheckboxGroup object

CheckboxGroup cg=new CheckboxGroup();

Then create each of the radio buttons Checkbox male=Checkbox(male,cg,true);

Checkbox female=Checkbox(female,cg,false);

Used as option button to specify choices.


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Example

Output


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Lists

User may select one or more items

Created using a number of strings or textvalues

Choice class enables us to create multipleitem lists

Choice moviestars=new Choice();

Add items using the addItem() method

moviestars.addItem(Antonio Banderas);

moviestars.addItem(Leonardo Dicaprio);

Displays a list of choices to the user


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Example

Output


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Event handling

with components (1)

Event Delegation Model is used to handleevents

This process allows the program to register

handlers called listeners with objects whoseevents need to be captured

Handlers are automatically called when an

event takes place

An event is generated whenever a user clicks amouse, presses or releases a key


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Event handling

with components (2)

Steps to be followed

Associate the class with the appropriate listenerinterface

Identify all components that generate events Identify all events to be handled

Implement the methods of the listener and writethe event handling code within the methods

Event listeners are implemented as interfaces

in Java


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Event handling

with components (3)Event Class Description Interface

ActionEvent Button is pressed, list item isdouble clicked or a menu isselected

ActionListener

AdjustmentEvent When scrollbar is used AdjustmentListener

ComponentEvent Component is resized,

moved, hidden or madevisible

ComponentListener

FocusEvent Component gains or loseskeyboard focus

FocusListener


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Event handling

with components (4)Event Class Description Interface

ItemEvent When a menu item is selectedor deselected or when a

checkbox or list item is clicked

ItemListener

WindowEvent Window is activated, closed,opened or quit

WindowListener

TextEvent Value of a text field or text areais changed

TextListener

MouseEvent Mouse is moved, clicked,dragged or released

MouseListener MouseMotionListener

KeyEvent Input is received from thekeyboard

KeyListener

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