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Why Java

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					    CSC 112

Intro to Computer
 Programming in
    JavaScript

    Spring 2005
  Internet and WWW
 Internet and WWW are     not the same –
  Internet includes email and other things

            the computers and the means
 Internet is
  by which they physically connect to each
  other.

 World Wide Web is    the logical means of
  accessing the files on these computers,
  primarily as web pages.
Using the World Wide Web
   Browsers
      Netscape Navigator
      Internet Explorer
   Plug-ins
      Java
      Macromedia Flash
      Acrobat Reader
        …
   Search Engines
      Yahoo and many others
  Internet Protocols
 TCP/IP –   Transmission Control Protocol
  / Internet Protocol
 FTP – File Transfer Protocol
 http – Hypertext Transfer Protocol
 telnet – for remote login to other
  computers, with local computer as dumb
  terminal
          IP Addresses
 Example –   123.45.67.89
 For specific computers on the Internet
 Information is passed between them in
  packets
 A named address (next slide) is converted to
  an IP address by a Domain Name Server
  (DNS)
        Named Addresses
URL’s – Uniform Resource Locators
http://www.music.sony.com/Music/index.html

http is the protocol
com is the domain – others are edu, org, gov, …
www. music.sony.com is the server computer
Music is the folder on the server computer
index.html is the file in the Music folder
 Hypertext Markup Language
 Describes with tags how web page should be
  formatted for display by browser
 Container tags, thus <BODY> and </BODY>
 Non container tags, thus <BR> or <HR>
 Tags must be properly nested
Basic Skeleton of an   HTML Page
        <HTML>
        <HEAD>
          <TITLE> … </TITLE>
        </HEAD>
        <BODY>
           …
        </BODY>
        </HTML>
Tags for Lists
For an unordered list
  <UL>
    <LI>
    <LI>
      …
 </UL>

For an ordered list
  <OL>
   <LI>
   <LI>
     …
  </OL>
 Attributes of HTML Tags
 Describe how to accomplish a result
 Attributes may or may not have values, as in
   <P ALIGN=left> …. </P>
 BODY attributes include   colors for links and
  for background
 FONT attributes include color and size
         Hypertext Links
 <A   HREF=“some URL“> anchor text </A>

 (Absolute or relative URL’s)

 <AHREF=“#fragment identifier”>
 anchor text </A>

 <A   NAME=“a named anchor”> </A>
    Images in Web Pages
                  page is loaded, with
 Images appear when
  <IMG SRC=“URL for image file”>

           for web pages are of type
 Image files
 GIF or JPG

         are loaded via links, with
 Image files
 <A HREF=“URL for image file”> some text </A>
             Programming
 The Client-Server Model
 Compiling versus Interpreting
 Embedding JavaScript code in a web page
 The Syntax or grammar of a P.L. (programming
  language)
  –   Variables – numbers and strings and booleans
  –   Operators – arithmetic and comparison
  –   Concatenating strings with the overloaded + operator
  –   Expressions – modifying precedence with parentheses
  –   Statements – the assignment operator, the terminal
      semicolon
Translating a Program to ML
 Assembler Language (AL)


 High Level Languages (HLL’s)
  Interpreting – Translate and execute on the fly
  Compiling – Translate source program to
    object program, then execute it, retaining
    translation for subsequent execution
      JavaScript Objects
Thus,
  var foo = new Object()

Objects may contain
  primitives of type number, string, or boolean
  other objects !
  methods, or functions
Thus,
  function foobar (){
       statement;
       statement;
            …
  }
Creating Forms with HTML
    <FORM … >
       <INPUT TYPE=text …>
       <INPUT TYPE=button …>
       <INPUT TYPE=reset …>
       <INPUT TYPE=checkbox …>
       <INPUT TYPE=radio …>
       <SELECT …>
          <OPTION …>
          <OPTION …>
            …
       </SELECT>
       <TEXTAREA …> </TEXTAREA>
    </FORM>
    Processing Forms
      with JavaScript
Events, such as onclick and onchange
Functions as event handlers
Local variables in functions
Converting strings to numbers with
 parseFloat()
Arrays, as with
  var numbers = new Array()
The elements array, automatically, for all of
 the items in the form
selectedIndex for pull-down menus
                  Arrays
 The array is   a special kind of object
           var foo = new Array ( );
  where the items in foo are indexed by integer
  values, thus
           foo[1], foo[j], foo[2*k+3]…
       first index value is 0, it is a standard
 If the
  array, as with elements[ ] and options[ ]
 A property of an array is its size, as with
  foo.length
Basic Tags for Tables
    <TABLE>
      <TR>
        <TD>
        <TD>
         …
      <TR>
        <TD>
        <TD>
         …
    </TABLE>
Attributes of TableTags
 <TABLE>   … </TABLE>
  ALIGN, BGCOLOR, BORDER, CELLPADDING,
  CELLSPACING, HEIGHT, WIDTH

 <TR>   … </TR>
  ALIGN, VALIGN, BGCOLOR

 <TD>   … </TD>
  ALIGN, VALIGN, BGCOLOR, COLSPAN,
  ROWSPAN
     Control Structures
 Sequential Processing
      do A, then B, then C, …
 Conditional Processing (branching or
  selection)
      if A is true, then do B, else do C
 Iterative Processing (looping or repetition)
      while A is true, do B {and test A again}
Conditional Processing
  Comparison operators
  Boolean variables
  Logical operators for and, or, not

     if (boolean condition) {
         statement;
         statement;
           …
     }
     else {
         statement;
         statement;
           …
     }
Iterative Processing
    Must have three components
      - Initialize the loop control variable (lcv)
      – Test the lcv for termination
      – Update the lcv to next value

    Thus, we have the for statement
       for (j = 0 ; j < 10 ; j += 1) {
          statement;
          statement;
       }

    We also have the while statement
        j = 0;
         while (j < 10) {
             statement;
             j += 1;
         }
  Understanding Iteration
 Word Problems
   To compute the number of days in the years 1950-2000
     days = 0;
      for (years = 1950 ; years <= 2000 ; years++)
         if (years % 4 == 0)
            days += 366;
         else
            days += 365;

 Tracing Iteration
     for (j = 1 ; j <= 3 ; j++)
         for (k = 0 ; k < j ; k++)
            document.write (j + “ ” + k + “<BR>”);
                   Functions
 Function   definition (in the HTML head), thus
       function foobar (a, b, c) {
          statement;
          statement;
       }
  where a,b,c are formal parameters.

 Function   invocation or function call, thus
       foobar (5, j, “Hello”);
  where the values in parentheses are actual parameters;
  when foobar is called, a=5, b=j, and c=“Hello”
                  Cookies
 Name   - Value pairs are just text strings!
 When server responds to client request, it
  sends cookie to be stored on client.
 When browser sends request to server, it
  retrieves cookie (if present) for server.
 The GOOD
   for customizing user interface to server
   for implementing shopping carts
 The BAD
   without user knowledge or consent
   contribute to junk mail and spamming
 JS codeto SetCookie(), GetCookie(),
  getCookieVal(), DeleteCookie()
    Sources of Errors
 Typing errors
 Syntax errors  – incorrect grammar
     syntax is how a message is given
 Logical errors – incorrect semantics
      semantics is the meaning
 Poor algorithms
 Bad input values – GIGO
 Incorrect specification of the problem
Computer Ethical Issues
  Privacy versus   security
  Spamming
  Emailusage
  Hacking
  Ownership and piracy
     …

				
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