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

Event handling
with components (2)
 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 handling
with components (3)
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 handling
with components (4)
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

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