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Applets and HTML MSTU 4031: Programming I 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. Sample Applets

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applets and html

Applets and HTML

MSTU 4031: Programming I

applets
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.
sample applets
Sample Applets
  • Heart Simulator
    • http://www.columbia.edu/ccnmtl/projects/heart/sim.html
  • Rice Virtual Statistics Lab
    • http://www.ruf.rice.edu/~lane/stat_sim/descriptive/index.html
  • Final Projects (Fall 2003)
    • http://www.columbia.edu/~lwk2103/mstu4031/Seasons/WinterOuter.html
    • http://www.columbia.edu/~yw2009/HealthEducation/
    • http://www.columbia.edu/~jh2284/mstu4031/finalproject/curve.html
the process of creating and displaying an applet
The Process of Creating and Displaying an Applet

Creates

Run & Display

.java

Compiler

.class

.html

Browser

Embed

Compile

applets security
Applets & Security
  • Applets run in a sandbox, where it can display information and get user input, but can’t read or touch anything on the user’s 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.
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.

init() like a no parameter constructor

paint() method is called whenever the surface of the applet needs to be filled in.

Difference between Applets and Console Applications
java applet package
java.applet Package

import java.applet.Applet;

public void init(){}

public void paint(Graphics g){}

java awt package
java.awt Package
  • 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
writing text to the screen
Console

(java.io.PrintStream)

method

println()

Applets

(java.awt.Graphics2D)

method

drawString()

Writing Text to the Screen
slide10

import java.applet.Applet;

import java.awt.Graphics;

public class MyApplet extends Applet

{

}

import java.awt.Graphics2D;

public void paint (Graphicsg)

{

}

Graphics2D g2 = (Graphics2D) g ;

g2.drawString ("Floor plan of a diner", 145, 20);

graphics2d class
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.
applet display properties
Applet Display Properties
  • Applet canvas is measured width and height (defined in <applet> tag in HTML)

<applet code = “MyClass.class” width=“300” height=“300”> </applet>

  • 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.
slide13

y

0 50 100 250 300 350 400 450 500 550 600

Origin

0

50

100

150

200

250

300

350

400

450

500

0,0

x, y

(100, 350)

x, y, w, h

(50, 400, 350, 100)

x

0 50 100 250 300 350 400 450 500 550 600

My Floor plan

Basepoint

graphical shapes
Graphical Shapes
  • Rectangles
  • Ellipses
  • Lines
  • Arcs

Example Floor Plan

slide15

import java.applet.Applet;

import java.awt.Graphics;

import java.awt.Graphics2D;

public class MyApplet extends Applet

{

}

import java.awt.Rectangle;

public void paint (Graphicsg)

{

}

Graphics2D g2 = (Graphics2D) g ;

Rectangleouterborder = new Rectangle (5, 30, 400, 300);

g2.draw(outerborder);

slide16

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 (Graphicsg)

{

}

Graphics2D g2 = (Graphics2D) g ;

Ellipse2D.Doubleseat1 = new Ellipse2D.Double

(50, 125, 20, 20);

g2.draw(seat1);

g2.drawString("S1",55,138);

slide17

import java.applet.Applet;

import java.awt.Graphics;

import java.awt.Graphics2D;

public class MyApplet extends Applet

{

}

import java.geom.Line2D;

public void paint (Graphicsg)

{

}

Graphics2D g2 = (Graphics2D) g ;

Line2D.Doublemyline = new Line2D.Double(5,50,400,50);

g2.draw(myline);

slide18

import java.applet.Applet;

import java.awt.Graphics;

import java.awt.Graphics2D;

public class MyApplet extends Applet

{

}

public void paint (Graphicsg)

{

}

Graphics2D g2 = (Graphics2D) g ;

// x, y, w, h, start angle, arc angle

g2.drawArc(300, 100, 50, 50, 90, 90);

about web pages
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.
slide20
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 (/).
sample html page
Sample HTML Page

<html>

<title>Title Here</title>

<h3>Text Here</h3>

<body>

</body>

</html>

running an applet
Running an Applet
  • To run an applet you need an HTML page with the applet tag.

<applet code = “ .class” width=“” height=“”> </applet>

  • The applet tag include the applet in a web page
  • Tell the browser where to find the applet code
sample html page with applet
Sample HTML Page With <applet>

<html>

<title>My First Applet! </title>

<applet code = “My.class” width=“400” height=“400”> </applet>

<h3>Look at my applet!</h3>

<body>

</body>

</html>

browser compatibility
Browser Compatibility
  • For applets to work on the latest versions of IE and Netscape you can not use the <applet></applet> tags.
  • Instead, insert this code: http://java.sun.com/products/plugin/1.3/docs/tags.html#Any
using parameters
Using Parameters
  • HTML
    • <PARAM NAME=“myText” VALUE”Hello!”>
  • JAVA
    • init()
      • This method is called when the applet is first loaded into the browser. It is used to perform applet initialization, in preference to a constructor method. You can either use a constructor or the init(). Create all GUI components in the either the constructor or init.
      • If you use a constructor, it must be a no-argument constructor. An applet gets its arguments from <PARAM> tags in the HTML file.
    • getParameterInfo()
      • this method is called to obtain information about the parameters to which the applet responds. Returns a String [][] that describes the parameters.
    • getParameter()
    • This method looks up and returns the value of the named parameter, specified with a <PARAM> tag in the HTML file that contains the applet.
sample floor plans
Sample Floor Plans
  • Floor Plans
    • http://www.columbia.edu/~rh506/mstu4031/hw7/FloorPlan.html
    • http://www.columbia.edu/~sc472/mstu4031/hw7/FloorPlan.html
    • http://www.columbia.edu/~mk2379/mstu4031/hw07/FloorPlan.html
    • http://www.columbia.edu/~lwk2103/mstu4031/hw7/FloorPlan.html
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