Applets, Graphical User Interfaces, and Threads

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Applets, Graphical User Interfaces, and Threads
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Interface ?

• an agent between two entities

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Interface
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Interface
gas
pump
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Interface
mortgage agent
dream house
you
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Interfaces
real interfaces

• ATM machine
• remote control
• bank teller
• browser (Netscape Navigator or Internet Explorer)

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Interfaces

• are designed to handle events initiated by user

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Events

• single click
• double click
• dragging

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Events

• An applet has mechanisms to handle events

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Applet

• A Java programs designed to run in a browser

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Applet

• applet class files are embedded in a HTML document

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Applet
all applets are subclasses of the applet class
public class SomeApplet extends Applet
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Applet
Applets differ from applications in that a
browser controls the applets execution
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Applet
the browser calls your applet's init() method
when the applet is started. An applet's start()
and stop() methods are called when the page where
the applet is running gains or loses focus.
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Why Restrict Applets ?

• An applet is code from another machine that you
  are not familiar

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Applet Restrictions

• cannot automatically send information to a users
  printer
• prevented from performing file operations
• prevented from certain network activities

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Applet Restriction Relaxed

• can be relaxed by changing the browsers security
  settings

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Applet Syntax
public class appletName extends Applet
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Sample Applet
import java.applet.Applet import
java.awt.Graphics public class Welcome extends
Applet public void paint(Graphics g)
g.drawString("Java is fuuuuuuuuuun )
...",25,25)
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Applets HTML File
ltapplet codeWelcome.class width215
height100gt lt/appletgt

• the HTML file name does not have to match the
  name of the class name as in the java file
• however, the class name in the applet code tag
  must match the class name

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Applets HTML File
ltapplet codeWelcome.class width215
height100gt lt/appletgt
the area of the applet is determined by the width
and height parameters
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Applet Template
import java.awt. import java.applet. public
class SampleApplet extends Applet public
void init() System.out.println("
SampleApplet.init() executed")
public void paint(Graphics g) public
void start() public void stop()
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Applets Life

• the browser manages the life cycle of the applet
• the life cycle includes the following
• init
• start
• stop
• destroy

• paint

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Applet Methods(init)

• called when an applet begins
• called once during the applets execution

• code to initialize the applet is placed in init()

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Applet Methods(start)

• called immediately after init()
• when the page where the applet is running gains
  focus

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Applet Methods(stop)

• called when the page where the applet is running
  loses focus

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Applet Methods(destroy)

• called when the browser terminates

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Applet Methods(paint)

• refreshes the browser display