Understanding Swing Components

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Understanding Swing Components

• Java Chapter 13
• Dr. James Jiang

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In this chapter, you will

• Use the JFrame class methods
• Use Swing event listeners
• Use JPanel class methods
• Use the JCheckBox class
• Use the ButtonGroup classes
• Create a drop-down list and combo box using the
  JComboBox class
• Create JScrollPanes
• Create JToolBars

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Using the JFrame Class

• GUI Components
• import javax.swing.
• Buttons, check boxes, are defined in the
  Component class
• Components widgets - windows gadgets
• You usually place components in the Containers
  class
• Container- type of component that holds other
  components.
• Usually takes the form of a window
• Defined in the Container class
• Use container to treat components as a single
  entity

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Using the JFrame

• The JFrame class is a Component class
• The JFrame is the best container option
• The setSize()
• The setVisible()
• The syntax to use any of these methods is
• JFrame object, a dot, and the method name
• JFrame aFrame new JFrame(This is a frame)
• aFrame.setSize(200, 100)
• aFrame.setVisible(true) (see p.468,
  Figure 13.7)

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Using Additional JFrame Class Methods

• A JFrames action in response to a user clicking
  -- is set by passing an argument to the
  setDefaultCloseOperation() method placed inside
  the JFrame constructor method
• EXIT_ON_CLOSE exists the program
• DISPOSE_ON_CLOSE closes the frame, disposes of
  the JFrame object, and keeps running the
  application
• DO_NOTHING_ON_CLOSE keeps the JFrame and
  continues running
• HIDE_ON_CLOSE closes the JFrame and continues
  running

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Using Swing Event Listeners

• Classes that respond to user events must
  implement an interface that deals with the events
• These interfaces are called event listeners
• Each listener can handle a specific event type
• A class can implement as many event listeners as
  needed

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Using Swing Event Listeners

• When a user event takes place, the appropriate
  method is automatically called.
• public void actionPerformed (ActionEvent event)
• Object source event.getSource( )
• if (source answerButton)
• //take answerButton action
• else if (source noresponseButton)
• // take nonResponseButton action
• else
• // take some other action

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Using JPanel Class Methods

• JPanel is the simplest Swing container add
  other components directly.
• Steps
• Create a JPanel object
• Add components to the JPanel using the add()
  method and the component as the argument
• Call the setContentPane() method with the JPanel
  object created to set the application's content
  pane

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JPanel example

• JPanel pane new JPanel( )
• JButton button JButton(Exit)
• pane.add(button)
• setContentPane(pane)

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Using JPanel Class Methods

• Swing components have a default size for the
  objects created
• A components size can be changed using the
  components setPreferredSize() method
• Dimension buttonSize new Dimension(200, 20)
• JButton bigButton new JButton()
• bigButton.setPreferredSize(buttonSize)

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Creat a JFrame with two JButtons within a JPanel
(i)

• Import javax.swing.
• Import java.awt.
• Import java.awt.event.
• Public class JChangeMessage extends JFrame
  implement actionListener
• JButton b1 new JButton(North)
• Button b2 new JButton(South)
• BorderLayout aBorder new Borderlayout()
• public JChangeMessage ( )
• super(Change Message)
• setDefaultCloseOperation(JFrame.EXIT_ON_CLOS
  E)
• JPanel pane new JPanel( )
• pane.setLayout(aBorder)
• setContentPane(pane)

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Creat a JFrame with two JButtons within a JPanel
(ii)

• pane.add(North, b1)
• pane.add(South, b2)
• b1.addActionLister(this)
• b2.addActionLister(this)
• public static void main(String args)
• JFrame aFrame new JChangeMessage()
• aFrame.setSize(275, 100)
• aFrame.setVisible(true)

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Creat a JFrame with two JButtons within a JPanel
(iii)

• public void actionPerformed(ActionEvent e)
• Object source e.getSource( )
• if (source b1)
• b1.setText(Event Handlers
  Incorporated)
• else if (source b2)
• b2.setText(Works fine!)

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Using the JCheckBox Class

• JCheckBox Class- Consists of a JLabel positioned
  beside a square
• You can click the square to display or remove a
  check mark
• JCheckBox cooktailBox new JCheckBox(Cocktails,
  false)
• JCheckBox dinnerBox new JCheckBox(Dinner,
  true)

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ItemsStateChanged Event

• public class JDemoCheckBox extends JFrame
  implements ItemListener
• public void itemStateChanged(ItemEvent e)
• Object source e.getItem( )
• if (source checkBox1)
• int select e.getStateChange( )
• if (select ItemEvent.SELECTED)
• // some statement regarding
  selected
• else
• // some actions regarding the
  dis-selected
• if (source checkBox2)

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Using the ButtonGroup Classes

• ButtonGroup Classes
• can group several JCheckBoxes so a user can
  select only one at a time
• all other JCheckBoxes are automatically turned
  off when the user selects any one checkbox
• Either create a ButtonGroup and then create the
  individual JCheckBoxes, or you can create the
  JCheckBoxes and then create the Button group

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ButtonGroup examples

• JCheckBox beefBox new JCheckBox(Beef, false)
• JCheckBox fishBox new JCheckBox(Fish, false)
• ButtonGroup dinnerGroup new ButtonGroup()
• dinnerGroup.add(beefBox)
• dinnerGroup.add(fishBox)
• pane.add(beefBox)
• pane.add(fishBox)
• If dinnerGroup.isSelected() // to test if
  anyone is selected
• dinnerGroup.setSelected(beefBox) // set beefBox
  to be selected

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Example (p.475-484)

• public class JDemoButtonGroup extends JFrame
  implements itemListener
• JCheckBox dinnerBox new JCheckBox(Dinner,
  true)
• JCheckBox beefBox new JCheckBox(Beef,
  false)
• JCheckBox fishBox new JCheckBox(Fish,
  false)
• JLabel ePrice new JLabel(Event Price
  Estimate)
• JLabel totPrice new JLabel( The estimated
  total price is )
• public void main(String args)
• JFrame aFrame new JDemoButtonGroup( )
• aFrame.setSize (200, 150)
• aFrame.setVisible(True)

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Continue

• Public JDemoButtonGroup( )
• super(Check Box)
• setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE)
  
• JPanel pane new JPanel()
• pane.setLayout(new FlowLayout() )
• setContentPane(pane)
• pane.add(dinnerBox)
• pane.add(beefBox)
• pane.add(fishBox)
• pane.add(ePrice)
• pane.add(totPrice)

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Continue

• ButtonGroup dinnerGroup new ButtonGroup( )
• dinnerGroup.add(dinnerBox)
• dinnerGroup.add(beffBox)
• dinnerGroup.add(fishBox)
• dinnerBox.addItemListener(this)
• beefBox.addItemListener(this)
• fishBox.addItemListener(this)

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Continue

• public void itemStateChanged(ItemEvent check)
• Object source check.getItem( )
• if (source dinnerBox)
• int select check.getStateChange( ) //
  retrieve the check status
• if (select ItemEvent.SELECTED)
• totPrice.setText(Total price is
  500)
• else if (select ItemEvent.DESELECTED)
• totPrice.setText(Total price is
  )
• if (source fishBox)
• if (source beefBox)

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Creating a Drop-Down List and Combo Box Using the
JComboBox Class

• ComboBox - for picking items from a list or
  entering text into a field
• Drop-down list -- a choice list

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Creating a Drop-Down List and Combo Box Using the
JComboBox Class

• You can build a JComboBox by using a constructor
  with no arguments
• Then adding items to the list with the addItem()
  method
• JComboBox majorChoice new JComboBox( )
• majorChoice.addItem(Management Information
  Systems)
• majorChoice.addItem(Education)
• majorChoice.addItem(Marketing)
• majorChoice.addItemListener(this) // implement
  event handler
• pane.add(majorChoice) // add the drop-down list
  to the JPanel container
• majorChoice.setEditable(true) // Combox allow
  user to enter text

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More examples

• public void itemStateChanged (ItemEvent list)
• Object source list.getSource( )
• if (source favorBox ) //
  favorBox is a ComboBox
• int favorNum favorBox.getSelectedIn
  dex( )
• totalPrice favorPricefavorNum
• Where int favorPrice 0, 725, 325, 125,
  135
• int totalPrice 0

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Creating JScrollPanes

• A JScrollPane is a container whose methods can be
  used to hold any component that can be scrolled
• Add a JTextArea component to use both multiple
  rows and columns

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JScrollPane forms

• The JScrollPane constructor takes one of four
  forms
• JScrollPane() creates an empty JScrollPane where
  both horizontal and vertical scrollbars appear
  when needed
• JScrollPane(Component) creates a JScrollPane that
  displays the contents of the specified component
• JScrollPane(Component, int, int) creates a
  JScrollPane that displays the specified
  component, vertical scrollbar, and horizontal
  scrollbar.
• JScrollPane(int, int) creates a scroll pane with
  specified vertical and horizontal scrollbars

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Horizontal and vertical scrollbar constants

• HORIZONTAL_SCROLLBAR_AS_NEEDED
• HORIZONTAL_SCROLLBAR_ALWAYS
• HORIZONTAL_SCROLLBAR_NEVER
• VERTICAL_SCROLLBAR_AS_NEEDED
• VERTICAL_SCROLLBAR_ALWAYS
• VERTICAL_SCROLLBAR_NEVER
• JTextArea area new JTextArea(10, 40)
• JScrollPane scroll new JScrollPane (area,
  VERTICAL_SCROLLBAR_ALWAYS, HORIZONTAL_SCROLLBAR_N
  EVER)

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More examples

• JTextArea area new JTextArea(10, 40)
• JScrollPane scroll new JScrollPane(area)
• pane.add(scroll)
• setContentPane(pane)
• Where JPanel pane new JPanel()

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Creating JToolBars

• A Swing GUI can be designed so that a user can
  move a toolbar from one section of a graphical
  user interface to another section
• This type of toolbar is called dockable toolbar
• The process that allows you to move and then
  attach the toolbar is called docking
• A toolbar is created in Swing with the JToolBar
  class

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Creating JToolBars

• Constructor methods for the JToolBar class
  include the following
• JToolBar() creates a new toolbar that will line
  up components in a horizontal direction
• JToolBar(int) creates a new toolbar with a
  specified orientation of horizontal or vertical
• JToolBar tbar new JToolBar(SwingConstants.VERTIC
  AL)
• JButton b1 new JButton()
• Tbar.add(b1) // add items to a JToolBar

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Examples

• BorderLayout bord new BorderLayout( )
• JToolBar tbar new JToolBar(SwingConstants.VERTIC
  AL)
• ImageIcon image1 new ImageICon(dining.gif)
• JButton b1 newJButton(Dinning, image1)
• tbar.add(b1)
• b1.addActionListener(this) // event handling
• (see page 495)
• pane.setLayout(bord)
• pane.add(tbar, BorderLayout.NORTH)

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More examples

• public void actionPerformed(ActionEvent e)
• Object source e.getSource()
• if (source b1)
• edit.append(This is Button 1
  Example)
• if (source b2)
• edit.append(This is Button 2 Example)
• Where JTextArea edit new JTextArea(8, 30)