Lecture 02 Object Oriented Programming

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Lecture 09Abstract Windows Toolkit (AWT) and
Swing Components
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Outline

• GUI Interface
• JAVA Graphics API
• Event Handling
• Layout Managers
• JComponents

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GUI Interface

• Web-based application use a graphical user
  interface (GUI)
• The graphical components are bundled in a library
  known as the Abstract Window Toolkit (AWT)
• Mapped to the platform-specific components
• Heavyweight components

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Why swing?

• The appearance and how the user interacts with
  the program are known as that programs look and
  feel.
• javax.swing API makes the look and feel of GUI
  the same across platforms (lightweight component)

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GUI
java.lang.Object
java.awt.Component
java.lang.Container
java.swing.JComponent
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The Java Graphics API

Classes in the java.awt
AWTEvent



LayoutManager
package

Heavyweight


Fon
t

FontMetrics

Object

Color

Panel

Applet

JApplet

Graphics

Component

Container

Frame

Window

JFrame



Dialog

JDialog

JComponent

Swing Components

in the javax.swing package


Lightweight
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Java Graphics API

• Component
• A superclass of all user interface classes
• Container
• Used to group components
• A layout manager is used to position and place
  components in a container in the desired location
  and style
• JComponent
• A super class of all the lightweight
• JFrame
• This is a window nor contained inside another
  window
• It is a container that holds another Swing
  user-interface components

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Java Graphics API

• Jdialog
• A popup window or message box generally used as a
  temporary window to receive additional
  information from the user or to provide
  notification that an event has occurred
• JApplet
• A subclass of Applet
• You must extend JApplet to create a Swing-based
  Java Applet
• Jpanel
• An invisible container that holds user-interface
  components
• Panel can be nested

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Java Graphics API

• Graphics
• An abstract class that provides a graphical
  context for drawing lines and simple shapes
• Color
• A class deals with the colors of graphics
  components
• Font
• Usef for drawings in Grphics
• FontMetrics
• An abstract class used to get the properties of
  the fonts used in drawings

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Graphic Classes Classification

• Container classes
• JFrame, JPanel, and JApplet
• Component classes
• Subclasses of JComponent
• JButton, JTextField, JTextArea, JComboBox, JList,
  JRadioButton, and JMenu
• Helper classes
• Classes used by components and containers to draw
  and place objects
• Graphics, Color, Font, FontMetrics, Dimension,
  and Layout Managers

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JComponent
.


JCheckBoxMenuItem

JMenuItem

JMenu

JButton

AbstractButton

.JRadioButtonMenuItem

.JToggleButton

JCheckBox

JRadioButton

JComponent

.JEditorPane

.JTextField

.JTextComponent

.JPasswordField

.JT
extArea

.JCo
mboBox

.JList

.JMenuBar

.JOptionPane

.JFileChooser

.JScrollBar

.JScrollPane

.JPanel

.JLabel

.JPopupMenu

.JPane

.JSeparator

.JSlider

.JTabbedPane

.JRootPane

.JProgressBar

.JSplitPane

.JTable

.JToolBar

.JTree

.JColorChooser

.JInternalFrame

.JLayeredPane

.JTableHeader

.JToolTip

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Frames

• Frame is a window that is not contained inside
  another window. Frame is the basis to contain
  other user interface components in Java graphical
  applications.
• The Frame class can be used to create windows.

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JFrame

• Two constructors
• public JFrame ( )
• Creates an untitled JFrame object
• public JFrame( String title)
• Create a JFrame object with a specific title

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JFrame Methods

• setVisible (true)
• The frame is not visible until setVisible (true)
  method is applied
• setSize (int, int)
• Specify the frame size
• setDefaultCloseOperation (Jframe.EXIT_ON_CLOSE)
• Tells the program to terminate when the frame is
  closed

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Example Creating JFrame
import javax.swing. public class MyFrame
public static void main(String args)
JFrame frame new JFrame("Test Frame")
frame.setSize(400, 300) frame.setVisible(true
) frame.setDefaultCloseOperation(
JFrame.EXIT_ON_CLOSE)
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Creating Frame

• By default, a frame is displayed in the
  upper-left corner of the screen.
• To display a frame at a specified location, you
  can use the setLocation(x, y) method in the
  JFrame class. This method places the upper-left
  corner of a frame at location (x, y).

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Centering Frames

Screen

(x, y)

Frame

screenHeight

frameHeight

frameWidth

screenWidth

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Centering Frames

• Toolkit class
• the abstract superclass of all actual
  implementations of the AWT
• getScreenSize( )
• Can be used to obtain screens width and height
• Dimension class
• Encapsulates the width and height of a component
• get.Size method
• Get the size of Dimension object
• Return dimension of the object
• JFrame
• setLocation (x, y)

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Example

• CenterFrame

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Event-Driven Programming

• An event can be defined as a type of signal to
  the program that something has happened.
• The event is generated by external user actions
  such as mouse movements, mouse button clicks, and
  keystrokes, or by the operating system, such as a
  timer
• The GUI component on which an event is generated
  is called the source object
• E.g.
• A button is the source object for a
  clicking-button action event

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Event Classes
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Selected User Actions
Source Event TypeUser Action Object Generated Cl
icked on a button JButton ActionEvent Changed
text JTextComponent TextEvent Double-clicked on a
list item JList ActionEvent Selected or
deselected an item JList ItemEvent with a single
click Selected or deselected an
item JComboBox ItemEvent
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Event Handling Model

• GUI event information is stored in an object of a
  class that extends AWTEvent
• A program performs two key tasks
• Event listener
• An object of a class that implements one or more
  the event-listener interface from package
  java.awt.event
• Event handler
• A method that is automatically called in response
  to a particular type of event

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Event Handling Model

• Each event-listener interface specifies one or
  more event handling methods that must be defined
  in the class that implements the event-listener
  interface
• The use of event listeners is known as the
  delegation event model

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The Delegation Model
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Selected Event Handlers
Event Class Listener Interface Listener Methods
(Handlers)ActionEvent ActionListener actionPerfor
med(ActionEvent) ItemEvent ItemListener itemStateC
hanged(ItemEvent) WindowEvent WindowListener windo
wClosing(WindowEvent) windowOpened(WindowEvent)
windowIconified(WindowEvent) windowDeiconified
(WindowEvent) windowClosed(WindowEvent) window
Activated(WindowEvent) windowDeactivated(WindowE
vent)

• Look at the handout

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Inner Class

• Classes can be defined inside other classes
• Inner classes are used mainly in event handling
• Inner classes with names have the file name
• OuterClassNameInnerClassName.class

Public class A extends B public class
ActionEventHandler implements ActionLister publ
ic void actionPerformed ( ActionEvent
e)
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Anonymous Inner Class

• Anonymous inner class (class without a name)
• Anonymous inner class have the file name
  OuterClassName.class
• starts at 1 and is incremented for each
  anonymous inner class encountered during
  compilation

Window.addWindowListner( new WindowAdapter( )
public void windowClosing( WindowEvent
e) System.exit(0) )
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JLabel

• A subclass of Jcomponent
• A label is a display area for a short text, an
  image, or both. The non-default constructors for
  labels are as follows
• JLabel(String text, int horizontalAlignment)
• JLabel(String text)
• JLabel(Icon icon)
• JLabel(Icon icon, int horizontalAlignment)

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Text Components

• Use text component when you want to both display
  and input information
• JTextField
• Allows only a single line of text
• JTextArea
• Allows multiple lines of text

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JTextField

• A text field is an input area where the user can
  type in characters.
• Text fields are useful in that they enable the
  user to enter in variable data (such as a name or
  a description).
• A text field can display information like a label

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JTextField Constructors

• JTextField(int columns)
• Creates an empty text field with the specified
  number of columns.
• JTextField txtName new JTextField (20)
• JTextField(String text)
• Creates a text field initialized with the
  specified text.
• JTextField(String text, int columns)
• Creates a text field initialized with the
  specified text and the column size.
• JTextField (String, int maximumNumberCharaters)

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JTextField Methods

• getText()
• Returns the string from the text field.
• setText(String text)
• Puts the given string in the text field.
• setEditable(boolean editable)
• Enables or disables the text field to be edited.
  By default, editable is true.
• setColumns(int)
• Sets the number of columns in this text field.
  The length of the text field is changeable.

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JTextArea

• If you want to let the user enter multiple lines
  of text, you cannot use text fields unless you
  create several of them. The solution is to use
  JTextArea, which enables the user to enter
  multiple lines of text.

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JTextArea Constructors

• JTextArea( )
• Default constructor
• Create an empty text area
• JTextArea(int rows, int columns)
• Creates a text area with the specified number of
  rows and columns.
• JTextArea(String s, int rows, int columns)
• Creates a text area with the initial text andthe
  number of rows and columns specified.

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JTextArea Method

• Append method
• Allows to add information to the end of the
  string in a text area
• Use append method to build your output as the
  information becomes available to create multiple
  lines of output
• General Format
• componentName.append(String)
• Example
• txaInovice.append(Sold to strName)

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Container

• The onscreen display area has a content pane to
  which the GUI components must be attached so they
  can be displayed at execution time
• The content pane is an object of class Container
  from the java.awt package
• Container c getContentPane()

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JPanel

• Panels act as smaller containers for grouping
  user interface components
• JPanel p new JPanel()
• Adding component to a JPanel
• add method
• E.g.
• add(ComponentName)

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JButton

• A button is a component that triggers an action
  event when clicked. The following are JButton
  non-default constructors
• JButton(String text)
• JButton(String text, Icon icon)
• JButton(Icon icon)
• All button types are subclasses of AbstractButton
  from javax.swing package
• Button types
• Command buttons, check boxes, and radio buttons
• A command button gegnerates an ActionEvent
• When the user clicks the button with the mouse

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Responding to Jbutton Event

• public void actionPerformed(ActionEvent e)
• // Get the button label
• JoptionPane.showMessageDialog (null, You
  pressed
• 
  e.getActionCommnad() )

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Layout Managers

• Javas layout managers provide a level of
  abstraction to automatically map your user
  interface on all windowing systems.
• The UI components are placed in containers. Each
  container has a layout manager to arrange the UI
  components within the container.
• FlowLayout
• GridLayout
• BorderLayout
• CardLayout
• GridBagLayout

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FlowLayout Manager

• The components are arranged in the container from
  left to right in the order in which they were
  added. When one row becomes filled, a new row is
  started.
• FlowLayout Constructors
• public FlowLayout(int align, int hGap, int vGap)
• Constructs a new FlowLayout with a specified
  alignment, horizontal gap, and vertical gap. The
  gaps are the distances inpixel between
  components.
• public FlowLayout(int alignment)
• Constructs a new FlowLayout with a specified
  alignment and a default gap of five pixels for
  both horizontal and vertical.
• public FlowLayout()
• Constructs a new FlowLayout with a default center
  alignment and a default gap of five pixelsfor
  both horizontal and vertical.

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BorderLayout Manager

• The BorderLayout manager divides the window into
  five areas East, South, West, North, and Center.
  
• Components are added to a BorderLayout
• add(Component, constraint), where constraint is
  BorderLayout.East, BorderLayout.South,
  BorderLayout.West", BorderLayout.North", or
  BorderLayout.Center.

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GridLayout Manager

• The GridLayout manager arranges components in a
  grid (matrix) formation with the number of rows
  and columns defined by the constructor. The
  components are placed in the grid from left to
  right starting with the first row, then the
  second, and so on.

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GridLayout Constructors

• public GridLayout(int rows, int columns)
• Constructs a new GridLayout with the specified
  number of rows and columns.
• public GridLayout(int rows, int columns, int
  hGap, int vGap)
• Constructs a new GridLayout with the specified
  number of rows and columns, along with specified
  horizontal and vertical gaps between components.

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Example

• Tax Systems
• Add List
• Payroll Systems

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JCheckBox

• A check box is a component that enables the user
  to toggle a choice on or off, like a light
  switch.
• JCheckBox constructors
• JCheckBox(), JCheckBox(String text),
• JCheckBox(String text, boolean selected),
• JCheckBox(Icon icon), JCheckBox(String text, Icon
  icon)
• JCheckBox(String text, Icon icon, boolean
  selected)
• Requires using ItemListner
• Provides for objects whose states change from
  true of false
• Requires itemStateChanged( ) method
• Example

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JRadioButton

• Radio buttons are variations of check boxes. They
  are often used in the group, where only one
  button is checked at a time.
• JRadioButton constructors
• JRadioButton(), JRadioButton(String text)
• JRadioButton(String text, boolean selected),
  JRadioButton(Icon icon)
• JRadioButton(String text, Icon icon)
• JRadioButton(String text, Icon icon, boolean
  selected)
• Example JRadioButton

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JComboBox

• A combo box is a simple list of items from which
  the user can choose. It performs basically the
  same function as a list, but can get only one
  value. To create a choice, use its default
  constructor
• JComboBox()
• Add items to the list with the addItem( ) method
• JComboBox ( ) myChoice new JComboBox ( )
• myChoice.addItem (English)
• myChoice.addItem (Math)

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JComboBox

• JComboBox class method
• String getItemAt (int) Returns the text of the
  list item at the index position specified by the
  integer argument
• String getSelectedItem( ) returns the text of
  the currently selected item
• Int getItemCount( ) returns the number of items
  in the list
• Int getSelectedIndex( ) returns the item in the
  list that matches the given item
• void setMaximumRowCount (int) sets the maximum
  number of combo box rows that are displayed at
  one time

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JComboBox

• Treat items as an array
• Use the getSelectedIndex( ) method to determine
  the list position of the currently selected item
• E.g.
• String course English, History,
  Math
• int choice myChoice.getSelectedIndex( )

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JScrollPane

• Common to add a JTextArea component
• Constructors
• JScrollPane( )
• Creates where both horizontal and vertical
  scrollbars when needed
• JScrollPane(Component)
• Creates a JScrollPane that displays the contents
  of the specified component
• E.g
• JTextArea output new JTextArea( )
• JScrollPane scroll new JScrollPane (output)

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Menus

• Java provides several classesJMenuBar, JMenu,
  JMenuItem, JCheckBoxMenuItem, and
  JRadioButtonMenuItem to implement menus in a
  frame
• A JFrame or JApplet can hold a menu bar to which
  the pull-down menus are attached. Menus consist
  of menu items that the user can select (or toggle
  on or off). Menu bars can be viewed as a
  structure to support menus.

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Menu Demo
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The JMenuBar Class

• A menu bar holds menus the menu bar can only be
  added to a frame. Following is the code to create
  and add a JMenuBar to a frame

JFrame f new JFrame() f.setSize(300,
200) f.setVisible(true) JMenuBar mb new
JMenuBar() f.setJMenuBar(mb)
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The Menu Class

• You attach menus onto a JMenuBar. The following
  code creates two menus, File and Help, and adds
  them to the JMenuBar mb

JMenu fileMenu new JMenu("File") JMenu
helpMenu new JMenu("Help") mb.add(fileMenu) mb
.add(helpMenu)
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The JMenuItem Class

• You add menu items on a menu. The following code
  adds menu items and item separators inmenu
  fileMenu

fileMenu.add(new JMenuItem("new")) fileMenu.add(n
ew JMenuItem("open")) fileMenu.add(new
JMenuItem("-")) fileMenu.add(new
JMenuItem("print")) fileMenu.add(new
JMenuItem("exit")) fileMenu.add(new
JMenuItem("-"))
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Submenus

• You can add submenus into menu items. The
  following code adds the submenus Unix, NT,
  and Win95 into the menu item Software.

JMenu softwareHelpSubMenu new
JMenu("Software") JMenu hardwareHelpSubMenu
new JMenu("Hardware") helpMenu.add(softwareHelpSu
bMenu) helpMenu.add(hardwareHelpSubMenu) softwar
eHelpSubMenu.add(new JMenuItem("Unix")) softwareH
elpSubMenu.add(new JMenuItem("NT")) softwareHelpS
ubMenu.add(new JMenuItem("Win95"))
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Submenu Demo
Example
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JPopupMenus

• A subclass of JComponent
• Provide options that are specific to the
  component for which the popup trigger event was
  generated