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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)
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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
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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
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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
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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
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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
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Example
Output
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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
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Hierarchy of classes in Java
Component
Button Checkbox Container Choice Canvas
TextComponent
Label
Panel Window
Applet Frame Dialog
TextArea TextField
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Various components
Label Text field
Checkbox
Radio button
Button
Text Area
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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
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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 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
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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 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.
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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 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
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Example
Output
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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
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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
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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
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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