SSD3 Unit 3

1

• SSD3 Unit 3
• Introduction to Java Components
• Presentation 3.2A
• Website http//www.icarnegie.com

2
GUI Applications

• Download and open Example1.java from
• www.bscheele.com/ssd3
• Many similarities between GUI applications and
  applets
• Both extend a class
• public class MyApplet extends Applet
• public class MyApplication extends Frame
• Both use classes in the java.awt package
  (abstract windowing toolkit) and java.awt.event
  package
• import java.awt.
• import java.awt.event.

3
GUI Applications

• Both are windows
• Application is a Frame frame is window that has
• title bar
• menu bar
• borders
• resizing corners
• Applet is a Panel Panel is window that does not
  have
• title bar
• menu bar
• borders

4
Difference

• Applet uses init method to create window
• public void init() code to add and arrange
  components
• Application uses a different mechanism
• public class MyApplication extends Frame
• public static void main (String args)
• MyApplication application new
  MyApplication()
• application.show() // by default, window is
  invisible
• public MyApplication() // constructor
• setSize(width, height) // by default, width
  0 and height 0
• // code to add and arrange components

5
GUI Applications

• Both use same component classes
• TextField and TextArea
• Label
• Button
• Checkbox
• Checkbox and CheckboxGroup (radio buttons)
• List

6
GUI Applications

• Both use add method to add components to window
• add(new Label(First name))
• Both use setLayout method to change window layout
• setLayout(new FlowLayout())
• setLayout(new GridLayout(2, 3))
• Difference
• Default layout for Applet is FlowLayout
• Default layout for Application is BorderLayout

7
GUI Applications

• Both use paint method to draw graphics in window
• public void paint(Graphics g) to code to draw
  graphics
• The paint method is called automatically when
  window is created
• Both use repaint method to re-draw graphics in
  window
• public void actionPerformed(ActionEvent e)
• repaint()
• The repaint method is called automatically when
  window is damaged

8
GUI Applications

• Both use same mechanism to handle button clicks
• public class MyApplet extends Applet implements
  ActionListener
• public void init()
• Button b new Button(Click me)
• b.addActionListener(this)
• public void actionPerformed(ActionEvent e)
  code to handle click
• public class MyApplication extends Frame
  implements ActionListener
• public MyApplication()
• Button b new Button(Click me)
• b.addActionListener(this)
• public void actionPerformed(ActionEvent e) code
  to handle click

9
GUI Applications

• Both use same mechanism to handle event caused
  when cursor is in text field and user hits Enter
  key
• public class MyApplet extends Applet implements
  ActionListener
• public void init()
• TextField field new TextField ()
• field.addActionListener(this)
• public void actionPerformed(ActionEvent e)
  code to handle event
• public class MyApplication extends Frame
  implements ActionListener
• public MyApplication()
• TextField field new TextField ()
• field.addActionListener(this)
• public void actionPerformed(ActionEvent e) code
  to handle event

10
GUI Applications

• When user clicks close box in upper left corner
  of window, window should shut down
• No special code needed for applet
• Application must have code to handle this
  WindowEvent
• Application must add seven methods
• All are empty except WindowClosing, the one that
  handles the event caused when user clicks the
  close button

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GUI Applications

• public class MyApplication extends Frame
• implements ActionListener,
  WindowListener
• public MyApplication()
• addWindowListener(this)
• public void windowOpened(WindowEvent e)
• public void windowClosing(WindowEvent e)
  System.exit(0)
• public void windowClosed(WindowEvent e)
• public void windowIconified(WindowEvent e)
• public void windowDeiconified(WindowEvent e)
• public void windowActivated(WindowEvent e)
• public void windowDeactivated(WindowEvent e)

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GUI Applications

• Will only deal with three events in unit 1
• user clicks button
• user presses Enter key button while cursor is in
  text field
• user clicks close box in upper left corner of
  window

13
GUI applications

• GUI applications in detail
• layout
• components
• event handling
• Layout determines how components are arranged in
  window
• SSD3 introduces a new layout class BorderLayout

14
BorderLayout

• Window divided into 5 regions
• East
• West
• North
• South
• Center
• Bring up Javadoc for BorderLayout
• Must specify region when adding a component (see
  example code in Javadoc)
• If no region is specified, component is added to
  Center (see exampel code in Javadoc)
• Components expand to fill region

15
Components

• SSD3 will use a small subset
• Label
• Button
• TextField
• TestArea
• List
• Checkbox

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Components

• Label
• Constructors
• Label ( String )
• Label (String , alignment )
• Methods
• setText (String )
• Button
• Constructor
• Button ()

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TextFields

• Constructors
• TextField ( )
• TextField (String )
• TextField (String , characters wide )
• Methods
• setText (String )
• String getText( )

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TextAreas

• Constructors
• TextArea ( rows, chars wide )
• TextArea (String , rows, chars wide )
• TextArea (String , rows, chars wide,
  scrollbars )
• Methods
• setText (String ) overwrites existing text
• append (String ) adds new text to end of
  existing text
• String getText ( )

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Lists

• Default selection is single selection
• Constructors
• List ( ) creates default list with 4 items
  visible
• List ( how-many-items-visible-at-one-time )
• Methods
• add (String ) adds item to list
• String getSelectedItem ( )
• int getSelectedIndex ( ) first element in list
  has index 0

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Checkbox

• Used to create checkboxes
• Constructors
• Checkbox ( Check me) - unchecked
• Checkbox ( Check me, true) checked
• Methods
• boolean getState ( ) true if checkbox is checked

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Checkbox

• Also used to create radio buttons
• Only one button can be selected at a time
• Constructors
• CheckboxGroup group new CheckboxGroup()
• Checkbox ( red, group, false) not selected
• Checkbox ( green, group, true) selected
• Checkbox ( blue, group, false) not selected
• Methods
• boolean getState ( ) true if radio button is
  selected

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Event Handling

• Application registers as listener for button
• b.addActionListener ( this )
• Application has implements ActionListener
  clause
• public class MyApplication extends Frame
  implements ActionListener
• Application defines actionPerformed method to
  handle event (button click)
• public void actionPerformed(ActionEvent e)
• JVM creates ActionEvent object when user clicks
  button
• JVM passes ActionEvent object to Button object
• Button object calls applications actionPerformed
  method
• Look at Example1.java and Example2.java

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Event Handling

• Buttons do not process event
• A button keeps a list of listeners
• Listeners are applications/applets that want to
  be alerted when the user clicks the button
• Button passes ActionEvent object to listener(s)
  for processing
• This is achieved by button calling the listeners
  actionPerformed method

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Event Handling

• Methodology called delegation event model
• Advantages
• Code to process events separated from code that
  detects events
• Only objects interested in events are notified
  when event occurs
• Any number of objects can be easily notified when
  an event occurs

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Event listeners

• Similar process for other events caused by user
  interactions with application
• Application registers as a listener with the
  component
• Application adds code so application is a
  listener
• implements xxxListener clause in class header
• adds method(s) to handle events caused when user
  interacts with component
• listener class defines the methods that must be
  implemented
• Many types of Listeners and each listener has a
  unique set of methods
• See Javadoc for EventListener

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GUI application summary

• Three logical parts to GUI application
• Constructor (five logical sub-tasks)
• Give window height width
• Change layout if border layout not appropriate
• Instantiate components
• Add components to window
• Register application as listener for events
• Main method
• Create instance of application class
• Display application
• Event handling methods

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Starting Point JFrame

• Content pane
• JFrame uses content pane in same way as does
  JApplet.
• Auto-close behavior
• JFrames close automatically when you click on the
  Close button (unlike AWT Frames). However,
  closing the last JFrame does not result in your
  program exiting the Java application. So, your
  main JFrame still needs a WindowListener to
  call System.exit. Or, alternatively, if using JDK
  1.3 or later, you can call setDefault-CloseOperati
  on(EXIT_ON_CLOSE). This permits the JFrame to
  close however, you wont be able to complete any
  house cleaning as you might in the
  WindowListener.
• Look and feel
• The default look and feel is Java (Metal)

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JFrame Example Code

• import java.awt.
• import javax.swing.
• public class JFrameExample
• public static void main(String args)
• WindowUtilities.setNativeLookAndFeel()
• JFrame f new JFrame("This is a test")
• f.setSize(400, 150)
• Container content f.getContentPane()
• content.setBackground(Color.white)
• content.setLayout(new FlowLayout())
• content.add(new JButton("Button 1"))
• content.add(new JButton("Button 2"))
• content.add(new JButton("Button 3"))
• f.addWindowListener(new ExitListener())
• f.setVisible(true)

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JFrame Helper ExitListener

• import java.awt.
• import java.awt.event.
• public class ExitListener extends WindowAdapter
• public void windowClosing(WindowEvent event)
• System.exit(0)

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JFrame Example Output
31
Swing Equivalents of AWT Components

• JLabel
• New features HTML content images, borders
• JButton
• New features icons, alignment, mnemonics
• JPanel
• New feature borders
• JSlider
• New features tick marks and labels

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JLabel

• Main new feature HTML content
• If text is "lthtmlgt...lt/htmlgt", it gets rendered
  as HTML
• HTML labels only work in JDK 1.2.2 or later, or
  in Swing 1.1.1 or later.
• In JDK 1.2 the label string must begin with
  lthtmlgt, not ltHTMLgt. It is case-insensitive in JDK
  1.3 and 1.4.
• JLabel fonts are ignored if HTML is used. If you
  use HTML, all font control must be performed by
  HTML.
• You must use ltPgt, not ltBRgt, to force a line
  break.
• Other HTML support is spotty.
• Be sure to test each HTML construct you use.
  Permitting the user to enter HTML text at runtime
  is asking for trouble.
• Other new features images, borders

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JLabel Example Code

• String labelText
• "lthtmlgtltFONT COLORWHITEgtWHITElt/FONTgt and "
• "ltFONT COLORGRAYgtGRAYlt/FONTgt Textlt/htmlgt"
• JLabel coloredLabel
• new JLabel(labelText, JLabel.CENTER)
• ...
• labelText
• "lthtmlgtltBgtBoldlt/Bgt and ltIgtItaliclt/Igt
  Textlt/htmlgt"
• JLabel boldLabel
• new JLabel(labelText, JLabel.CENTER)
• labelText
• "lthtmlgtThe Applied Physics Laboratory is..."
• "of the Johns Hopkins University."
• "ltPgt" ... "...lt/htmlgt"

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JLabel Example Output
35
JButton

• Main new feature icons
• Create an ImageIcon by passing the ImageIcon
  constructor a String representing a GIF or JPG
  file (animated GIFs are supported!).
• From an applet, call getImage(getCodeBase())
  normally, then pass resultant Image to ImageIcon.
• Pass the ImageIcon to the JButton constructor.
• Alternatively, call setIcon. In fact, there are 7
  possible images (rollover images, images for when
  button is depressed, etc.)
• Other features
• HTML content as with JLabel
• Alignment location of image with respect to text
  
• Mnemonics keyboard accelerators that let you use
  Alt-someChar to trigger the button.

36
JButton Example Code

• import java.awt.
• import javax.swing.
• public class JButtons extends JFrame
• public static void main(String args)
• new JButtons()
• public JButtons()
• super("Using JButton")
• WindowUtilities.setNativeLookAndFeel()
• addWindowListener(new ExitListener())
• Container content getContentPane()
• content.setBackground(Color.white)
• content.setLayout(new FlowLayout())

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JButton Example Code (Continued)

• JButton button1 new JButton("Java")
• content.add(button1)
• ImageIcon cup new ImageIcon("images/cup.gif"
  )
• JButton button2 new JButton(cup)
• content.add(button2)
• JButton button3 new JButton("Java", cup)
• content.add(button3)
• JButton button4 new JButton("Java", cup)
• button4.setHorizontalTextPosition
• (SwingConstants.LEFT)
  
• content.add(button4)
• pack()
• setVisible(true)

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JButton Example Output
39
JPanel

• Main new feature borders
• Create a Border object by calling
  BorderFactory.createXxxBorder.
• Supply the Border object to the JPanel by means
  of setBorder.
• JPanel p new JPanel()
• p.setBorder(BorderFactory.createTitledBorder("Java
  "))
• Other features
• Layout manager settings
• Can pass the layout manager to the JPanel
  constructor
• Setting preferred size
• There is no JCanvas. If you want JPanel to act
  like Canvas, call setPreferredSize.

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Standard Borders

• Static methods in BorderFactory
• createEmptyBorder(int top, int left, int bottom,
  int right)
• Creates an EmptyBorder object that simply adds
  space (margins) around the component.
• createLineBorder(Color color)
• createLineBorder(Color color, int thickness)
• Creates a solid-color border
• createTitledBorder(String title)
• createTitledBorder(Border border, String title)
• The border is an etched line unless you
  explicitly provide a border style in second
  constructor.
• createEtchedBorder()
• createEtchedBorder(Color highlight, Color shadow)
• Creates a etched line without the label

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JPanel Example Code

• public class SixChoicePanel extends JPanel
• public SixChoicePanel(String title, String
  buttonLabels)
• super(new GridLayout(3, 2))
• setBackground(Color.lightGray)
• setBorder(BorderFactory.createTitledBorder(tit
  le))
• ButtonGroup group new ButtonGroup()
• JRadioButton option
• int halfLength buttonLabels.length/2
• for(int i0 ilthalfLength i)
• option new JRadioButton(buttonLabelsi)
• group.add(option)
• add(option)
• option new JRadioButton(buttonLabelsihal
  fLength)
• group.add(option)
• add(option)

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JPanel Example Output

• Left window uses createLineBorder
• Right window has three SixChoicePanels

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Questions?