awt information

Abstract Windowing Toolkit

Session 3

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)


Introduction

These make the language richer in terms of creating graphical objects that can be controlled by the developer as well as the user.

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

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

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


Abstract Windowing Toolkit

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

AWT provides items which enable creation of an attractive and efficient GUI

Graphical User Interface (GUI) is used to accept input through a keyboard or a mouse


Containers

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

directly or indirectly derives two commonly used containers – Frame and Panel

Frame is a separate window and has borders Panel is an area without borders and is

contained within a window

An area that can hold elements


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


Example

Output


Containers - Panel

Simplest way to create a panel is through its constructor 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 include scrollbars, scrollpanes and dialogs

Anything that can be placed on a user interface and can be made visible or resized


Hierarchy of classes in Java

Component

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


Example

Output


TextArea

Includes a scrollbar TextArea can be created using some of the following

constructors given below: TextArea( )

Creates a new TextArea TextArea(int rows, int cols)

Creates a new TextArea with given number of rows and columns 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


Example

Output


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


Example

Output


Checkbox

Checkboxes in Java can be created using constructors.

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 user may select or deselect by clicking them.


Example

Output


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.


Example

Output


Lists

User may select one or more items Created using a number of strings or text

values Choice class enables us to create multiple

item 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


Example

Output


Event handling with components (1)

Event Delegation Model is used to handle events

This process allows the program to register handlers called ‘listeners’ with objects whose events need to be captured

Handlers are automatically called when an event takes place

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



Steps to be followed – Associate the class with the appropriate listener

interface Identify all components that generate events Identify all events to be handled Implement the methods of the listener and write

the event handling code within the methods

Event listeners are implemented as interfaces in Java



Event Class Description Interface

ActionEvent Button is pressed, list item is double clicked or a menu is selected

ActionListener

AdjustmentEvent When scrollbar is used AdjustmentListener

ComponentEvent Component is resized, moved, hidden or made visible

ComponentListener

FocusEvent Component gains or loses keyboard focus

FocusListener



Event Class Description Interface

ItemEvent When a menu item is selected or 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 area is changed

TextListener

MouseEvent Mouse is moved, clicked, dragged or released

MouseListener Mouse MotionListener

KeyEvent Input is received from the keyboard

KeyListener

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Java Language Fundamentals / 30 of 28

awt information

Education

new button

panel frame

given alignment

used containers frame

containers frame

given title

given number of rows

following constructors