Wednesday, October 7, 2015

Introduction to web development





Internet             The Internet is the global system of interconnected computer networks that use the Internet protocol suite (TCP/IP) to link billions of devices worldwide.

                      A Brief History
                     of the Internet

     The Internet was the result of some visionary thinking by people in the early 1960s who saw great potential value in allowing computers to share information on research and development in scientific and military fields. J.C.R. Licklider of MIT first proposed a global network of computers in 1962, and moved over to the Defense Advanced Research Projects Agency (DARPA) in late 1962 to head the work to develop it. Leonard Kleinrock of MIT and later UCLA developed the theory of packet switching, which was to form the basis of Internet connections. Lawrence Roberts of MIT connected a Massachusetts computer with a California computer in 1965 over dial-up telephone lines. It showed the feasibility of wide area networking, but also showed that the telephone line's circuit switching was inadequate. Kleinrock's packet switching theory was confirmed. Roberts moved over to DARPA in 1966 and developed his plan for ARPANET. These visionaries and many more left unnamed here are the real founders of the Internet.
When the late Senator Ted Kennedy heard in 1968 that the pioneering Massachusetts company BBN had won the ARPA contract for an "interface message processor (IMP)," he sent a congratulatory telegram to BBN for their ecumenical spirit in winning the "interfaith message processor" contract.
The Internet, then known as ARPANET, was brought online in 1969 under a contract let by the renamed Advanced Research Projects Agency (ARPA) which initially connected four major computers at universities in the southwestern US (UCLA, Stanford Research Institute, UCSB, and the University of Utah). The contract was carried out by BBN of Cambridge, MA under Bob Kahn and went online in December 1969. By June 1970, MIT, Harvard, BBN, and Systems Development Corp (SDC) in Santa Monica, Cal. were added. By January 1971, Stanford, MIT's Lincoln Labs, Carnegie-Mellon, and Case-Western Reserve U were added. In months to come, NASA/Ames, Mitre, Burroughs, RAND, and the U of Illinois plugged in. After that, there were far too many to keep listing here.

Who was the first to use the Internet?

Charley Kline at UCLA sent the first packets on ARPANet as he tried to connect to Stanford Research Institute on Oct 29, 1969. The system crashed as he reached the G in LOGIN!
The Internet was designed to provide a communications network that would work even if some of the major sites were down. If the most direct route was not available, routers would direct traffic around the network via alternate routes.
The early Internet was used by computer experts, engineers, scientists, and librarians. There was nothing friendly about it. There were no home or office personal computers in those days, and anyone who used it, whether a computer professional or an engineer or scientist or librarian, had to learn to use a very complex system.

Did Al Gore invent the Internet?

According to a CNN transcript of an interview with Wolf Blitzer, Al Gore said,"During my service in the United States Congress, I took the initiative in creating the Internet." Al Gore was not yet in Congress in 1969 when ARPANET started or in 1974 when the term Internet first came into use. Gore was elected to Congress in 1976. In fairness, Bob Kahn and Vint Cerf acknowledge in a paper titled Al Gore and the Internet that Gore has probably done more than any other elected official to support the growth and development of the Internet from the 1970's to the present .
E-mail was adapted for ARPANET by Ray Tomlinson of BBN in 1972. He picked the @ symbol from the available symbols on his teletype to link the username and address. The telnet protocol, enabling logging on to a remote computer, was published as a Request for Comments (RFC) in 1972. RFC's are a means of sharing developmental work throughout community. The ftp protocol, enabling file transfers between Internet sites, was published as an RFC in 1973, and from then on RFC's were available electronically to anyone who had use of the ftp protocol.
Libraries began automating and networking their catalogs in the late 1960s independent from ARPA. The visionary Frederick G. Kilgour of the Ohio College Library Center (now OCLC, Inc.) led networking of Ohio libraries during the '60s and '70s. In the mid 1970s more regional consortia from New England, the Southwest states, and the Middle Atlantic states, etc., joined with Ohio to form a national, later international, network. Automated catalogs, not very user-friendly at first, became available to the world, first through telnet or the awkward IBM variant TN3270 and only many years later, through the web. See The History of OCLC

Ethernet, a protocol for many local networks, appeared in 1974, an outgrowth of Harvard student Bob Metcalfe's dissertation on "Packet Networks." The dissertation was initially rejected by the University for not being analytical enough. It later won acceptance when he added some more equations to it.
The Internet matured in the 70's as a result of the TCP/IP architecture first proposed by Bob Kahn at BBN and further developed by Kahn and Vint Cerf at Stanford and others throughout the 70's. It was adopted by the Defense Department in 1980 replacing the earlier Network Control Protocol (NCP) and universally adopted by 1983.
The Unix to Unix Copy Protocol (UUCP) was invented in 1978 at Bell Labs. Usenet was started in 1979 based on UUCP. Newsgroups, which are discussion groups focusing on a topic, followed, providing a means of exchanging information throughout the world . While Usenet is not considered as part of the Internet, since it does not share the use of TCP/IP, it linked unix systems around the world, and many Internet sites took advantage of the availability of newsgroups. It was a significant part of the community building that took place on the networks.
Similarly, BITNET (Because It's Time Network) connected IBM mainframes around the educational community and the world to provide mail services beginning in 1981. Listserv software was developed for this network and later others. Gateways were developed to connect BITNET with the Internet and allowed exchange of e-mail, particularly for e-mail discussion lists. These listservs and other forms of e-mail discussion lists formed another major element in the community building that was taking place.
In times past, it was fascinating to watch a BITNET message we sent as it proceeded from one stop to the next along the way to its destination. We would see it arrive at a site and then see it transmitted along to the next site and the next site and the next. The pace of life was slower then!
In 1986, the National Science Foundation funded NSFNet as a cross country 56 Kbps backbone for the Internet. They maintained their sponsorship for nearly a decade, setting rules for its non-commercial government and research uses.
As the commands for e-mailFTP, and telnet were standardized, it became a lot easier for non-technical people to learn to use the nets. It was not easy by today's standards by any means, but it did open up use of the Internet to many more people in universities in particular. Other departments besides the libraries, computer, physics, and engineering departments found ways to make good use of the nets--to communicate with colleagues around the world and to share files and resources.
While the number of sites on the Internet was small, it was fairly easy to keep track of the resources of interest that were available. But as more and more universities and organizations--and their libraries-- connected, the Internet became harder and harder to track. There was more and more need for tools to index the resources that were available.
The first effort, other than library catalogs, to index the Internet was created in 1989, as Peter Deutsch and Alan Emtage, students at McGill University in Montreal, created an archiver for ftp sites, which they named Archie. This software would periodically reach out to all known openly available ftp sites, list their files, and build a searchable index of the software. The commands to search Archie were unix commands, and it took some knowledge of unix to use it to its full capability.

McGill University, which hosted the first Archie, found out one day that half the Internet traffic going into Canada from the United States was accessing Archie. Administrators were concerned that the University was subsidizing such a volume of traffic, and closed down Archie to outside access. Fortunately, by that time, there were many more Archies available.
At about the same time, Brewster Kahle, then at Thinking Machines, Corp. developed his Wide Area Information Server (WAIS), which would index the full text of files in a database and allow searches of the files. There were several versions with varying degrees of complexity and capability developed, but the simplest of these were made available to everyone on the nets. At its peak, Thinking Machines maintained pointers to over 600 databases around the world which had been indexed by WAIS. They included such things as the full set of Usenet Frequently Asked Questions files, the full documentation of working papers such as RFC's by those developing the Internet's standards, and much more. Like Archie, its interface was far from intuitive, and it took some effort to learn to use it well.
Peter Scott of the University of Saskatchewan, recognizing the need to bring together information about all the telnet-accessible library catalogs on the web, as well as other telnet resources, brought out his Hytelnet catalog in 1990. It gave a single place to get information about library catalogs and other telnet resources and how to use them. He maintained it for years, and added HyWebCat in 1997 to provide information on web-based catalogs.
In 1991, the first really friendly interface to the Internet was developed at the University of Minnesota. The University wanted to develop a simple menu system to access files and information on campus through their local network. A debate followed between mainframe adherents and those who believed in smaller systems with client-server architecture. The mainframe adherents "won" the debate initially, but since the client-server advocates said they could put up a prototype very quickly, they were given the go-ahead to do a demonstration system. The demonstration system was called a gopher after the U of Minnesota mascot--the golden gopher. The gopher proved to be very prolific, and within a few years there were over 10,000 gophers around the world. It takes no knowledge of unix or computer architecture to use. In a gopher system, you type or click on a number to select the menu selection you want.
Gopher's usability was enhanced much more when the University of Nevada at Reno developed the VERONICA searchable index of gopher menus. It was purported to be an acronym for Very Easy Rodent-Oriented Netwide Index to Computerized Archives. A spider crawled gopher menus around the world, collecting links and retrieving them for the index. It was so popular that it was very hard to connect to, even though a number of other VERONICA sites were developed to ease the load. Similar indexing software was developed for single sites, called JUGHEAD(Jonzy's Universal Gopher Hierarchy Excavation And Display).
Peter Deutsch, who developed Archie, always insisted that Archie was short for Archiver, and had nothing to do with the comic strip. He was disgusted when VERONICA and JUGHEAD appeared.
In 1989 another significant event took place in making the nets easier to use. Tim Berners-Lee and others at the European Laboratory for Particle Physics, more popularly known as CERN, proposed a new protocol for information distribution. This protocol, which became the World Wide Web in 1991, was based on hypertext--a system of embedding links in text to link to other text, which you have been using every time you selected a text link while reading these pages. Although started before gopher, it was slower to develop.
The development in 1993 of the graphical browser Mosaic by Marc Andreessen and his team at the National Center For Supercomputing Applications (NCSA) gave the protocol its big boost. Later, Andreessen moved to become the brains behind Netscape Corp., which produced the most successful graphical type of browser and server until Microsoft declared war and developed its MicroSoft Internet Explorer.
Soon after the graphical browser Mosaic was introduced, the Library of Congress made available some wonderful graphics of the colorful illustrated Vatican Scrolls. With the slow connections of those days, it would take 20 minutes for a single page to load. We would start the download, go on coffee break, and return and marvel at picture that had filled our screen.
Since the Internet was initially funded by the government, it was originally limited to research, education, and government uses. Commercial uses were prohibited unless they directly served the goals of research and education. This policy continued until the early 90's, when independent commercial networks began to grow. It then became possible to route traffic across the country from one commercial site to another without passing through the government funded NSFNet Internet backbone.
Delphi was the first national commercial online service to offer Internet access to its subscribers. It opened up an email connection in July 1992 and full Internet service in November 1992. All pretenses of limitations on commercial use disappeared in May 1995 when the National Science Foundation ended its sponsorship of the Internet backbone, and all traffic relied on commercial networks. AOL, Prodigy, and CompuServe came online. Since commercial usage was so widespread by this time and educational institutions had been paying their own way for some time, the loss of NSF funding had no appreciable effect on costs.

MICHAEL DERTOUZOS
1936-2001

The early days of the web was a confused period as many developers tried to put their personal stamp on ways the web should develop. The web was threatened with becoming a mass of unrelated protocols that would require different software for different applications. The visionary Michael Dertouzos of MIT's Laboratory for Computer Sciences persuaded Tim Berners-Lee and others to form the World Wide Web Consortium in 1994 to promote and develop standards for the Web. Proprietary plug-ins still abound for the web, but the Consortium has ensured that there are common standards present in every browser.
Read Tim Berners-Lee's tribute to Michael Dertouzos.
Today, NSF funding has moved beyond supporting the backbone and higher educational institutions to building the K-12 and local public library accesses on the one hand, and the research on the massive high volume connections on the other.
Microsoft's full scale entry into the browser, server, and Internet Service Provider market completed the major shift over to a commercially based Internet. The release of Windows 98 in June 1998 with the Microsoft browser well integrated into the desktop shows Bill Gates' determination to capitalize on the enormous growth of the Internet. Microsoft's success over the past few years has brought court challenges to their dominance. We'll leave it up to you whether you think these battles should be played out in the courts or the marketplace.
During this period of enormous growth, businesses entering the Internet arena scrambled to find economic models that work. Free services supported by advertising shifted some of the direct costs away from the consumer--temporarily. Services such as Delphi offered free web pages, chat rooms, and message boards for community building. Online sales have grown rapidly for such products as books and music CDs and computers, but the profit margins are slim when price comparisons are so easy, and public trust in online security is still shaky. Business models that have worked well are portal sites, that try to provide everything for everybody, and live auctions. AOL's acquisition of Time-Warner was the largest merger in history when it took place and shows the enormous growth of Internet business! The stock market has had a rocky ride, swooping up and down as the new technology companies, the dot.com's encountered good news and bad. The decline in advertising income spelled doom for many dot.coms, and a major shakeout and search for better business models took place by the survivors.
A current trend with major implications for the future is the growth of high speed connections. 56K modems and the providers who supported them spread widely for a while, but this is the low end now. 56K is not fast enough to carry multimedia, such as sound and video except in low quality. But new technologies many times faster, such as cablemodems and digital subscriber lines (DSL) are predominant now.
Wireless has grown rapidly in the past few years, and travellers search for the wi-fi "hot spots" where they can connect while they are away from the home or office. Many airports, coffee bars, hotels and motels now routinely provide these services, some for a fee and some for free.
A next big growth area is the surge towards universal wireless access, where almost everywhere is a "hot spot". Municipal wi-fi or city-wide access, wiMAX offering broader ranges than wi-fi, EV-DO, 4g, LTE, and other formats will joust for dominance in the USA in the years ahead. The battle is both economic and political.
Another trend that is rapidly affecting web designers is the growth of smaller devices to connect to the Internet. Small tablets, pocket PCs, smart phones, ebooks, game machines, and even GPS devices are now capable of tapping into the web on the go, and many web pages are not designed to work on that scale.
As the Internet has become ubiquitous, faster, and increasingly accessible to non-technical communities, social networking and collaborative services have grown rapidly, enabling people to communicate and share interests in many more ways. Sites like FacebookTwitterLinked-InYouTubeFlickrSecond Lifedelicious,blogswikis, and many more let people of all ages rapidly share their interests of the moment with others everywhere.
As Heraclitus said in the 4th century BC, "Nothing is permanent, but change!"
May you live in interesting times! (ostensibly an ancient Chinese curse)For more information on Internet history, visit these sites:

Internet Essentials

As we enter our fifth back-to-school season for Internet Essentials, we are more committed than ever to attack the digital divide in a meaningful way.  I’ve seen first-hand the power that the Internet has to transform lives, strengthen communities, and inspire a new generation of leaders.  It levels the playing field by creating greater access to education, health care, employment opportunities, news, information, and entertainment.
So, it gives us great pleasure to announce a number of new and exciting ways we are enhancing the program.  These changes come from our own learnings, as well as from feedback from our customers and nonprofit and governmental partners.  Since we first offered Internet Essentials in August 2011, we have now made 25 enhancements to the program.  Highlights from this year’s announcements include:  is a high level, dynamic, untyped, and interpreted programming language. It has been standardized in the ECMAScript language specification.
                HTML is a markup language for describing web documents (web pages). HTML stands for Hyper Text Markup Language. A markup language is a set of markup tags. HTML documents are described by HTML tags. Each HTML tag describes different document content.

Tuesday, October 6, 2015

introduction toProgramming

 
                      Computer Programming

      Computer programming (often shortened to programming) is a process that leads from an original formulation of a computing problem to executable computer programs.

  Program
            A computer program or app is a sequence of instructions, written to perform a specified task on a computer. A computer requires programs to function, typically executing the program's instructions in a central processor.
         It is step by step process instructions that directs the computer to do the tasks you want it to do and produce the results you want.
                      The programming Process
Defining the problem
          In almost every problem solving methodology the first step is defining or identifying the problem. It is the most difficult and the most important of all the steps.
            what it is you know (input-given data) and what it is you want to obtain (output-the resul
Planning the solution
        Planning Solutions provides expert advice and representation in all aspects of urban and regional planning.
                Planning the solution by using the flowchart and pseudo code.
Coding the program 
         express your solution in a programming language. You will translate the logic from the flowchart or pseudo code-or some other tool-to a programming language.
Testing the program
         various inputs and documenting what you have done.most programmers get used to the idea that their newly written programs probably have a few errors.
Documenting the program
                  necessary process, although, as many programmers are, you may be eager to pursue more exciting computer-centered activities.

                         Levels of Language
Machine language
          Machine code or machine language is a set of instructions executed directly by a computer's central processing unit (CPU). Each instruction performs a very specific task, such as a load, a jump, or an ALU operation on a unit of data in a CPU register or memory.
Assembly languages
       An assembly language (or assembler language) is a low-level programming language for a computer, or other programmable device, in which there is a very strong (generally one-to-one) correspondence between the language and the architecture's machine code instructions.
 High-level languages
       Ultimately, programs written in a high-level language must be translated into machine language by a compiler or interpreter. The firsthigh-level programming languages were designed in the 1950s. Now there are dozens of different languages, including Ada, Algol, BASIC, COBOL, C, C++, FORTRAN, LISP, Pascal, and Prolog.
Very high-level languages
        A very high-level programming language (VHLL) is a programming language with a very high level of abstraction, used primarily as a professional programmer ...
Natural languages
             In computing, natural language refers to a human language such as English, Russian, German, or Japanese as distinct from the typically artificial command or programming language with which one usually talks to a computer. The term usually refers to a written language but might also apply to spoken language.

Flowchart and Pseudo code
        Write a program that reads two numbers and displays the numbers in decreasing order
Algorithm    
   -a step-by-step procedure for solving a problem.An algorithm (pronounced AL-go-rith-um) is a procedure or formula for solving a problem. The word derives from the name of the mathematician,

Flowchart
      A flowchart is a type of diagram that represents an algorithm, workflow or process, showing the steps as boxes of various kinds, and their order by connecting them with arrows. This diagrammatic representation illustrates a solution model to a given problem.
         a picture of the separate steps of a process in sequential order.

Information Technology (Introduction)


INFORMATION TECHNOLOGY


What is a Information Technology?
                        The study or use of systems (especially computers and telecommunications) for storing, retrieving, and sending information.This is my course i take because i want to explore on programming. In this course is so very important nowadays. All business are related or needed a computer to become easiest and fastest doing our work. Despite also in communication it is so very easy to communicate our love ones through technology such us Facebook, tweeter and Instagram. I choose also this course because i want to learn on programming. Information technology is the use of any aspects like in job and a lot of more and also in computers, storage and networking and other physical devices, infrastructure and process, store, secure and exchange all forms of electronic data            Nowadays, many people play games. You can write about games you play and post updates and/or cheats/hints.               
            Stands for "Information Technology," and is pronounced "I.T." It refers to anything related to computing technology, such as networking, hardware, software, the Internet, or the people that work with these technologies. Many companies now have IT departments for managing the computers, networks, and other technical areas of their businesses. IT jobs include computer programming, network administration, computer engineering, Web development, technical support, and many other related occupations. Since we live in the "information age," information technology has become a part of our everyday lives. That means the term "IT," already highly overused, is here to stay.The world has become a "global village" due to advancement in IT.

What is a Computer?

      Are you new to computers? Do you wonder what they do and why you would want to use one? Welcome—you're in the right place. This article gives an overview of computers: What they are, the different types, and what you can do with them.
         A computer is an electronic device that manipulates information, or data. It has the ability to store, retrieve, and process data. You probably already know that you can use a computer to type documents, send email, play games, and browse the Web. You can also use it to edit or create spreadsheets, presentations, and even videos.Today's computers have both kinds of programming.
          Today, most people don't need to know how a computer works. Most people can simply turn on a computer or a mobile phone and point at some little graphical object on the display, click a button or swipe a finger or two, and the computer does something. An example would be to get weather information from the net and display it. How to interact with a computer program is all the average person needs to know.
           But, since you are going to learn how to write computer programs, you need to know a little bit about how a computer works. Your job will be to instruct the computer to do things.
         Computers are machines that perform tasks or calculations according to a set of instructions, or programs. The first fully electronic computers, introduced in the 1940s, were huge machines that required teams of people to operate. Compared to those early machines, today's computers are amazing. Not only are they thousands of times faster, they can fit on your desk, on your lap, or even in your pocket.










Basic Programming using Java

   
 Variables and Data types          
           Although you can create a complete database without writing code, in some cases, some tasks cannot be performed automatically. For these tasks, you must temporarily use values that you can change at will and dismiss when not needed anymore.
          A variable is a value that you "put" into the computer memory when necessary. The value is lost when the application closes. To proceed, you must communicate to the computer that you will need a portion of its memory to hold a certain value. When you communicate this, the computer reserves the necessary portion for you and makes it available when you need it.
            Communicating your intention is also referred to as declaring a variable. Because there can be various values used while the application is running, the computer would need two pieces of information to hold a value: a name that can be used to identify the portion of memory and the amount of memory that will be necessary to store the value.
           You often need to store values temporarily when performing calculations with Visual Basic. For example, you might want to calculate several values, compare them, and perform different operations on them, depending on the result of the comparison. You need to retain the values if you want to compare them, but you don't need to store them in a property.
        All variables in the Java language must have a data type. The Java language supports a full range of primitive data types, including integer,floating point, character, and boolean. In the example program, count is an integer, as indicated by the int keyword that precedes it.

                      
                JavaScript If...Else Statements


Conditional statement
        

    
                 In  computer science, conditional statements, conditional expressions and conditional constructs are features of a programming language which perform different computations or actions depending on whether a programmer-specified Boolean condition evaluates to true or false. Apart from the case of branch prediction,  this is always achieved by selectively altering the control flow based on some condition.
             In imperative programming languages, the term "conditional statement" is usually used, whereas in functional programming, the terms "conditional expression" or "conditional construct" are preferred, because these terms all have distinct meanings.


IF-statements 
        
          Before discussing the actual structure of the if statement, let us examine the meaning of TRUE and FALSE in computer terminology. A true statement is one that evaluates to a nonzero number. A false statement evaluates to zero.
             For example, the check 0 == 2 evaluates to 0. The check 2 == 2 evaluates to a 1. If this confuses you, try to use a cout statement to output the result of those various comparisons (for example cout<< ( 2 == 1 );)

Example

Make a "Good day" greeting if the hour is less than 18:00:
if (hour < 18) {
greeting = "Good day";
}

The else Statement


          Use the else statement to specify a block of code to be executed if the condition is false.
if (condition) {
block of code to be executed if the condition is true
} else {
block of code to be executed if the condition is false
}
Example
       If the hour is less than 18, create a "Good day" greeting, otherwise "Good evening":
if (hour < 18) {
greeting = "Good day";
} else {
greeting = "Good evening";
}

The else if Statement    

              Use the else if statement to specify a new condition if the first condition is false.
Syntax
if (condition1) {
block of code to be executed if condition1 is true
} else if (condition2) {
block of code to be executed if the condition1 is false and condition2 is true
} else {
block of code to be executed if the condition1 is false and condition2 is false
}
Example
        If time is less than 10:00, create a "Good morning" greeting, if not, but time is less than 20:00, create a "Good day" greeting, otherwise a "Good evening":
if (time < 10) {
greeting = "Good morning";
} else if (time < 20) {
greeting = "Good day";
} else {
greeting = "Good evening";
}

The if-then Statement         


          The if-then statement is the most basic of all the control flow statements. It tells your program to execute a certain section of code only if a particular test evaluates to true. For example, the Bicycle class could allow the brakes to decrease the bicycle's speed only if the bicycle is already in motion. One possible implementation of the applyBrakes method could be as follows:
void applyBrakes() { // the "if" clause: bicycle must be moving if (isMoving){ // the "then" clause: decrease current speed currentSpeed--; } }
            If this test evaluates to false (meaning that the bicycle is not in motion), control jumps to the end of the if-then statement.
           In addition, the opening and closing braces are optional, provided that the "then" clause contains only one statement:
void applyBrakes() { // same as above, but without braces if (isMoving) currentSpeed--; }


The if-then-else Statement   
             The if-then-else statement provides a secondary path of execution when an "if" clause evaluates to false. You could use an if-then-else statement in the applyBrakes method to take some action if the brakes are applied when the bicycle is not in motion. In this case, the action is to simply print an error message stating that the bicycle has already stopped.
void applyBrakes() { if (isMoving) { currentSpeed--; } else { System.err.println("The bicycle has already stopped!"); } }
                  The following program, if,else, assigns a grade based on the value of a test score: an A for a score of 90% or above, a B for a score of 80% or above, and so on.
class IfElseDemo {
 public static void main(String[] args) {
 int testscore = 76;
 char grade;
 if (testscore >= 90) { 
      grade = 'A'; 
 } else if (testscore >= 80) { 
      grade = 'B';
 } else if (testscore >= 70) {
      grade = 'C';
 } else if (testscore >= 60) {
      grade = 'D' 
 } else { grade = 'F';
 } 
 System.out.println("Grade = " + grade);
     
      }
 }

Looping statements

      Types of Loops. While a given expression is true it repeats the statement in the loop body. Before executing the loop body it tests the condition for true or false. It is like a while loop but it tests the condition after executing the loop body.

DATA TYPES

         In computer science and computer programming, a data type or simply type is a classification identifying one of various types of data, such as real, integer or Boolean, that determines the possible values for that type; the operations that can be done on values of that type; the meaning of the data; and the way values ...



                                          Java types

INTEGERS TYPE


byte:The byte data type is an 8-bit signed two's complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The byte data type can be useful for saving memory in large arrays, where the memory savings actually matters. They can also be used in place of int where their limits help to clarify your code; the fact that a variable's range is limited can serve as a form of documentation.

short: The short data type is a 16-bit signed two's complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). As with byte, the same guidelines apply: you can use a short to save memory in large arrays, in situations where the memory savings actually matters.
int: By default, the int data type is a 32-bit signed two's complement integer, which has a minimum value of -231 and a maximum value of 231-1. In Java SE 8 and later, you can use the int data type to represent an unsigned 32-bit integer, which has a minimum value of 0 and a maximum value of 232-1. Use the Integer class to use int data type as an unsigned integer. See the section The Number Classes for more information. Static methods like compare Unsigned, divide Unsigned etc have been added to the integer class to support the arithmetic operations for unsigned integers.
long: The long data type is a 64-bit two's complement integer. The signed long has a minimum value of -263 and a maximum value of 263-1. In Java SE 8 and later, you can use thelong data type to represent an unsigned 64-bit long, which has a minimum value of 0 and a maximum value of 264-1. Use this data type when you need a range of values wider than those provided by int. The long class also contains methods like compare Unsigned, divide Unsigned etc to support arithmetic operations for unsigned long.
        Each types has a maximum value, based on their binary representation:
–Bytes: 8-bits, ± 128
–Short: 16-bits, ± 215 ≈ 32,000
–Int: 32-bits, ± 231 ≈ 2 billion
–Long: 32-bits, ± 263 ≈ really big
FLOATING POINT (Decimal) TYPE

float: The float data type is a single-precision 32-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the floating-points types, format and values section of the Java Language Specification. As with the recommendations for byte and short, use a float (instead of double) if you need to save memory in large arrays of floating point numbers. This data type should never be used for precise values, such as currency. For that, you will need to use the  class instead.number and string covers Big Decimal and other useful classes provided by the Java platform.

double: The double data type is a double-precision 64-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the floating-points, types, format and values section of the Java Language Specification. For decimal values, this data type is generally the default choice. As mentioned above, this data type should never be used for precise values, such as currency.

    OTHER TYPES


Boolean: The Boolean data type has only two possible values: true and false. Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its "size" isn't something that's precisely defined.

char: The char data type is a single 16-bit Unicode character. It has a minimum value of '\u0000' (or 0) and a maximum value of 'f' (or 65,535 inclusive).
String:In computer programming, a string is traditionally a sequence of characters, either as a literal constant or as some kind of variable. The latter may allow its elements to be mutated and the length changed, or it may be fixed (after creation).

Friday, October 2, 2015

Introduction to Networking



INTRODUCTION TO NETWORKING


Computer Network Defined


            College life is one hell of a kind experience. You encounter things that you have been ignorant before. And honestly, I faced some difficulty in one of my subjects, the I.T. 11. Ironically, my course is Information Technology and I have difficulty in the subject of my field. But with just some few adjustments, I learned new yet useful information that I can use and apply in my life as an I.T. Professional.

         A computer network is a set of computers connected together for the purpose of sharing resources. The most common resource shared today is connection to the Internet. Other shared resources can include a printer or a file server.

A computer network is a group of computer systems and other computing hardware devices that are linked together through communication channels to facilitate communication and resource-sharing among a wide range of users. Networks are commonly categorized based on their characteristics.A computer network is a set of connected computers. Computers on a network are called nodes. The connection between computers can be done via cabling, most commonly the Ethernet cable, or wireless through radio waves. Connected computers can share resources, like access to the Internet, printers, file servers, and others. A network is a multipurpose connection, which allows a single computer to do more.

Network Architecture

             Network architecture refers to the layout of the network, consisting of the hardware, software, connectivity, communication protocols and mode of transmission, such as wired or wireless. Know about the types ofnetwork classified according to the areas covered such as LAN, MAN and WAN.
               Network Architecture is the overall design of a computer network that describes how a computer network is configured and what strategies are being used. It also known as network model or network design

       Two main network architecture: 

Client/Server network
            is a network architecture in which each computer or process on the network is either a client or a server. Servers are powerful computers or processes dedicated to managing disk drives (file servers), printers (print servers), or network traffic (network servers ).

Peer-To-Peer network
             is a commonly used computer networking architecture in which each workstation, or node, has the same capabilities and responsibilities. It is often compared and contrasted to tCablinghe classic client/server architecture, in which some computers are dedicated to serving others.


Ethernet Cabling

     to connect all devices in your network. Most modern networks use Category 5 or 6 cabling, and you can purchase the cables in a variety of lengths. You can even buy cables in different jacket colors to distinguish network devices in a large network. For instance, you can use blue cables for PCs, red ones for servers, and so on.

Modem
     a combined device for modulation and demodulation, for example, between the digital data of a computer and the analog signal of a telephone line.

Router and Switches
           Routers might have a single WAN port and a single LAN port and are designed to connect an existing LAN hub or switch to a WAN. Ethernet mac aDDswitches and hubs can be connected to a router with multiple PC ports to expand a LAN.

MAC Address
         A media access control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used as a network address for most IEEE 802 network technologies, including Ethernet and WiFi.

            Communication Device

 Hub  

  • A non-intelligent device, and has no decision making capability .Take the input data from one of the ports and broadcast the information to all the other ports connected to the network. 
 
Repeaters A repeater is a device similar to the Hub, but has additional features. Used in places where amplification of input signal is necessary Regenerates Faded Signals
Switch A switch is an intelligent device .Has a decision making capacity
Bridges A device that connects two local-area networks (LANs), or two segments of the same LAN that use the same protocol
Routers A router is a device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network.
NIC(Network Interface Card)  So that the computer can be connected to a network.



                                       Physical Topology

         Computer networks can be broken down historically into topological, which is a technique of connecting computers. The most common topology today is a collapsed ring. This is due to the success of a network protocol called the Ethernet. This protocol, or a network language, supports the Internet, Local Area Networks, and Wide Area Networks.

Star Topology

           star topology is a design of a network where a central node extends a cable to each computer on the network. On a star network, computers are connected independently to the center of the network. If a cable is broken, the other computers can operate without problems. A star topology requires a lot of cabling.

Bus Topology

          bus topology is another type of design where a single cable connects all computers and the information intended for the last node on the network must run through each connected computer. If a cable is broken, all computers connected down the line cannot reach the network. The benefit of a bus topology is a minimal use of cabling.

 Ring Topology

          A similar topology is called a ring. In this design, computers are connected via a single cable, but the end nodes also are connected to each other. In this design, the signal circulates through the network until it finds the intended recipient. If a network node is not configured properly, or it is down temporarily for another reason, the signal will make a number of attempts to find its destination.
collapsed ring is a topology where the central node is a network device called a hub, a router, or a switch. This device runs a ring topology internally and features plugins for cables. Next, each computer has an independent cable, which plugs into the device. Most modern offices have a cabling closet, or a space containing a switch device that connects the network. All computers in the office connect to the cabling closet and the switch. Even if a network plug is near a desk, the plug is connected via a cable to the cabling closet.
Mesh Topology
         A network setup where each computer and network device is interconnected with one another, allowing for most transmissions to be distributed, even if one of the connections go down. This topology is not commonly used for most computer networks as it is difficult and expensive to have redundant connection to every computer. However, this topology is commonly used for wireless network. Below is a visual example of a simple computer setup on a network using a mesh topology.


   There are two types of mesh topologies:

Full mesh topology: occurs when every node has a circuit connecting it to every other node in a network. Full mesh is very expensive to implement but yields the greatest amount of redundancy, so in the event that one of those nodes fails, network traffic can be directed to any of the other nodes. Full mesh is usually reserved for backbone networks.

Partial mesh topology: is less expensive to implement and yields less redundancy than full mesh topology. With partial mesh, some nodes are organized in a full mesh scheme but others are only connected to one or two in the network. Partial mesh topology is commonly found in peripheral networks connected to a full meshed backbone

TREE Topology

           It has a root node and all other nodes are connected to it forming a hierarchy. It is also called hierarchical topology. It should at least have three levels to the hierarchy.

HYBRID Topology

It is two different types of topology which is a mixture of two or more topology. For example if in an office in one department ring topology is used and in another star topology is used, connecting these topology will result in Hybrid Topology (ring topology and star topology).

There are two types of network, the Metropolitan Area Network and the Wide Area Network.




           First, let’s talk about the Metropolitan Area Network or what others call as MAN. It is a high speed network that connects local area network in Metropolitan Area such as city or town and handles bulk of communication activity across the region. A MAN typically includes one or more LAN but covers a smaller geographically area than a WAN.
                                   
                  The WAN or the Wide Area Network is a network that covers a large geographically area such country or the world. WAN combines many types of media such as telephone lines, cables and radio wave.

Network Architecture is the overall design of a computer network that describes and shows a computer network is configured and what strategies are being used. It also known as network model or network design.

            

A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, or office building.