Lecture 09 Applet and Advanced GUI

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Lecture 09Applet and Advanced GUI

• Jaeki Song

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Applet

• Applets run within the Web browser environment
• Applets bring dynamic interaction and live
  animation to an otherwise static HTML page
• Java is used not only as applets, but also as
  standalone applications and as a programming
  language for developing sever-side applications
• Applications and applets share many common
  programming features, although they differ
  slightly in some respects
• Every application must have a main method
• Java applets do not need a main method

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The Applet Class

• public class MyApplet extends JApplet
• public void init()
• ...
• public void start()
• ...
• public void stop()
• ...
• public void destroy()
• ...
• //your other methods

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Browser Calling Applet Methods
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The inti method

• Invoked when the applet is first loaded and again
  if the applet is reloaded.
• public void init( )
• can be seen and used by other
  classes and programs, such as the browser
• Common functions implemented in this method
  include loading images, setting up user-interface
  components, and getting parameters from the
  ltappletgt tag in the HTML page.

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The start method

• Invoked after the init() method is executed
  also called whenever the applet becomes active
  again after a period of inactivity
• For example, when the user returns to the page
  containing the applet after surfing other Web
  pages.

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The stop Method

• The opposite of the start() method, which is
  called when the user moves back to the page
  containing the applet the stop() method is
  invoked when the user moves off the page.

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The destroy Method

• Invoked when the browser exits normally to inform
  the applet that it is no longer needed and that
  it should release any resources it has allocated
• Usually, you will not need to override this
  method unless you need to release specific
  resources, such as threads that the applet
  created.

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The JApplet Class

• To use swing components, it is necessary to
  create a Java Applet that extends
  javax.swing.JApplet
• JApplet inherits all the methods from the Applet
  class

import javax.swing. public class Welcome
extends JApplet
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Writing Applets

• Always extends the JApplet class, which is a
  subclass of Applet for Swing components.
• Override init(), start(), stop(), and destroy()
  if necessary. By default, these methods are
  empty.
• Add your own methods and data if necessary.
• Applets are always embedded in anHTML page.

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Viewing Applets
lthtmlgt ltheadgt lttitlegt lt/headgt ltbodygt ltapplet co
de test.Welcome.class width 300 height
100gt lt/appletgt lt/bodygt lt/htmlgt
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Example

• HelloWorld
• Mortgage

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Applications vs. Applets

• Similarities
• Since they both are subclasses of the Container
  class, all the user interface components, layout
  managers, and event-handling features are the
  same for both classes.
• Differences
• Applications are invoked by the Java interpreter,
  and applets are invoked by the Web browser.
• Applets have security restrictions
• Web browser creates graphical environment for
  applets, GUI applications are placed in a frame.

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Font class

• Font constructor takes three arguments
• Font name, font style, and font size
• General Format
• Font (FontName, FontStyle, FontSize)
• Font fntName new Font (Sans Serif,
  Font.BOLD, 12)
• Methods
• getFont ( )
• setFont (Font f )
• Sets the current font to font, style, and size
  specified by the Font object reference f
• E.g
• lblName.setFont(fntName)

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The FontMetrics Class

• Can be used to know precise information about a
  font, such as height, descent, ascent, and leading

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FontMetrics Methods

• getAscent( )
• Return a value representing the ascent of a font
• getDescent( )
• Return a value representing the descent of a font
• getLeading( )
• Return a value representing the leading of a font
• getHeight( )
• Return a value representing the height of a font

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Color class

• Defines methods and constants for manipulating
  colors
• Pre-defined color
• RGB based 256 colors
• Constructors
• Three arguments
• Integer and float
• public Color (int r, int g, int b)
• public color (float r, float g, float b)

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Color Class Methods

• getRed( )
• Return a value between 0 to 255 representing the
  red content
• getGreen( )
• Return a value between 0 to 255 representing the
  green content
• getBlue( )
• Return a value between 0 to 255 representing the
  blue content
• getColor
• Return the current color
• setColor
• Sets the current color

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Changing the Color of Text

• setForeground method
• Changes the color of the letter
• E.g
• lblName.setForeground(Color.red)
• setBackground method
• Changes the background color
• E.g.
• setBackground(Color.cyan)
• Pre-defined colors
• black, blue, cyan, darkGray, gray, green, pink,
  lightGray, magenta, orange, red, white, yellow

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Example

• FontApplet

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Mouse Event

• Many actions taken by the user cause events to
  occur with mouse
• Click the mouse, move it over an object, move
  away from an object
• Java allows you to listen for mouse events using
  a MouseListner or MouseMotionListner

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Handling Mouse Events

• The MouseListener listens for actions such as
  when the mouse is pressed, released, entered,
  exited, or clicked.
• The MouseMotionListener listens foractions such
  as dragging or moving themouse.

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MouseEvent Handlers

• mouseEnter(MouseEvent e) and mouseExit(MouseEvent
  e)
• invoked when a mouse enters a component or exits
  the component
• mousePressed(MouseEvent e)
• Invoked when a mouse is pressed or released
• mouseClicked(MouseEvent e)
• Invoked when a mouse is pressed and then released
• mouseMoved(MouseEvent e)
• Invoked when the mouse is moved without being
  pressed

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Example

• MouseListener

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Keyboard Event Handling

• Key events are generated when key on the keyboard
  are pressed and released
• A class that implements KeyListener must provide
  definitions for method keyPressed, keyReleased
  and keyTyped

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InputEvent Methods

• public long getWhen( )
• Returns the time stamp indicating when the event
  occured
• public boolean isAltDown( )
• Returns true if the Alt key is down on the event
• public boolean isControlDown( )
• Returns true if the Control key is down on the
  event
• public boolean is MetaDown
• Returns true if the right mouse button is pressed
• public boolean is ShiftDown
• Returns true if the Shift key is down on the event

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Handling Keyboard Events
To process a keyboard event, use the following
handlers in the KeyListener interface

• keyPressed(KeyEvent e)
• Called when a key is pressed.
• keyReleased(KeyEvent e)
• Called when a key is released.
• keyTyped(KeyEvent e)
• Called when a key is pressed and then released.

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The KeyEvent Class

• Methods
• getKeyChar() method
• getKeyCode() method
• Keys
• Home VK_HOME
• End VK_End
• Page Up VK_PGUP
• Page Down VK_PGDN
• etc..

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Event Adapters

• Standard adapters
• Class that extends a convenience listener adapter
  or implements a listener interface
• Anonymous adapters
• The adapters implemented using inner classes

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Event Adapter Class and Interface
Event Adapter Class
Implements Interface
ComponentAdapter ContainerAdapter FocusAdapter Key
Adapter MouseAdapter MouseMotionAdapter WindowAdap
ter
CompoenentListerner ContainerListerner FocusLister
ner KeyListerner MouseListerner MouseMotionListern
er WindowListerner