Applets

1
Applets

• Applets are programs that run inside a web
  browser.
• The code for an applet is stored on a web server
  and downloaded into the browser whenever you
  access a web page with an applet.
• Applets are programmed as a class.

2
Applets Security

• Applets run in a sandbox, where it can display
  information and get user input, but cant read or
  touch anything on the users computer.
• You can give an applet more privileges (reading
  and writing local files), if you notify your
  browser that the applet is trusted.
• Applets can carry a certificate or signatures
  from an authentication firm (VeriSign) to tell
  you where the applet came from.

3
Difference between Applets and Console
Applications

• Console
• Runs from command line
• Text based
• Terminal window
• public static void main(String args)

• Applets
• Runs from browser
• Web based
• Graphical
• No main() method
• Reserved methods for Applets.
• paint() method is called whenever the surface of
  the applet needs to be filled in.

4
java.applet Package

• import java.applet.Applet
• public void paint(Graphics g)

5
java.awt

• java.awt package (abstract windowing toolkit)
• Defines many classes for graphics programming,
  mechanism for event handling, and a set of user
  interface components.
• java.awt.Graphics
• java.awt.Graphics2D

6
Writing Text to the Screen

• Console
• (java.io.PrintStream)
• method
• println()

• Applets
• (java.awt.Graphics2D
• method
• drawString()

7
import java.applet.Applet
import java.awt.Graphics
public class MyApplet extends
Applet
import java.awt.Graphics2D
public void paint (Graphics g)
Graphics2D g2 (Graphics2D) g
g2.drawString ("Floor plan of a diner", 145, 20)
8
Graphics2D Class

• Use the drawString () method to draw a string,
  starting at its basepoint.
• Use draw() method of the Graphics2D class to draw
  shapes such as rectangles, ellipses, line
  segments, polygons, and arcs.

9
Applet Display Properties

• Applet canvas is measured width and height
  (defined in ltappletgt tag in HTML)
• ltapplet code MyClass.class width300
  height300gt lt/appletgt
• Screen coordinates (x, y) and canvas size are
  measured in pixels.
• A pixel (picture element) is a dot on the screen.
• (10, 20) or (x, y ) is 10 pixels to the right
  and 20 pixels down from the top left corner of
  the panel.

10
My Floor plan
Basepoint
11
Graphical Shapes

• Rectangles
• Ellipses
• Lines
• Arcs

12
import java.applet.Applet import
java.awt.Graphics import java.awt.Graphics2D
public class MyApplet extends
Applet
import java.awt.Rectangle
public void paint (Graphics g)
Graphics2D g2 (Graphics2D) g
Rectangle outerborder new Rectangle (5, 30,
400, 300)
g2.draw(outerborder)
13
import java.applet.Applet import
java.awt.Graphics import java.awt.Graphics2D
public class MyApplet extends
Applet
import java.awt.geom.Ellipse2D
public void paint (Graphics g)
Graphics2D g2 (Graphics2D) g
Ellipse2D.Double seat1 new Ellipse2D.Double
(50, 125, 20, 20)
g2.draw(seat1) g2.drawString("S1",55,138)
14
import java.applet.Applet import
java.awt.Graphics import java.awt.Graphics2D
public class MyApplet extends
Applet
import java.geom.Line2D
public void paint (Graphics g)
Graphics2D g2 (Graphics2D) g
Line2D.Double myline new Line2D.Double(5,50,400,
50)
g2.draw(myline)
15
import java.applet.Applet import
java.awt.Graphics import java.awt.Graphics2D
public class MyApplet extends
Applet
public void paint (Graphics g)
Graphics2D g2 (Graphics2D) g
g2.drawArc(300, 100, 50, 50, 90, 90) // x, y, w,
h, start angle, arc angle
16
About Web Pages

• Web pages are written in Hypertext Markup
  Language (HTML)
• HTML files are made up of tags to format text
  (and include images, applets, audio and video
  files) that tell the browser how to render the
  text.

17
HTML

• Most HTML tags come in pairs with an opening and
  closing tag.
• Each pair applies to the text between the two
  tags.
• The closing tag is just like the opening tag, but
  it is prefixed by a slash (/).

18
Sample HTML Page

• lthtmlgt
• lttitlegtWeek 7 Example lt/titlegt
• lth3gtText Herelt/h3gt
• ltbodygt
• lt/bodygt
• lt/htmlgt

19
Running an Applet

• To run an applet you need an HTML page with the
  applet tag.
• ltapplet code .class width heightgt
  lt/appletgt
• The applet tag include the applet in a web page
• Tell the browser where to find the applet code