Introduction to HTML


What is HTML?

indroduction to HTML :: futureX
  • HTML is a language for describing web pages.
  • HTML stands for Hyper Text Markup Language
  • HTML is a markup language
  • A markup language is a set of markup tags
  • The tags describes document content
  • HTML documents contain HTML tags and plain text
  • HTML documents are also called web pages


 HTML Tags
  • HTML markup tags are usually called HTML tags
  • HTML tags are keywords (tag names) surrounded by angle brackets like <html>
  • HTML tags normally come in pairs like <b> and </b>
  • The first tag in a pair is the start tag, the second tag is the end tag
  • The end tag is written like the start tag, with a forward slash before the tag name
  • Start and end tags are also called opening tags and closing tags


                                      <tagname>content</tagname>
HTML Elements

 "HTML tags" and "HTML elements" are often used to describe the same thing.
But strictly speaking, an HTML element is everything between the start tag and the end tag, including the tags.
               <p>This is a paragraph.</p>
Web Browsers

 The purpose of a web browser (such as Google Chrome, Internet Explorer, Firefox, Safari) is to read HTML documents and display them as web pages. The browser does not display the HTML tags, but uses the tags to interpret the content of the page.

 HTML Versions

 Since the early days of the web, there have been many versions of HTML:
Version                        Year
HTML                          1991
HTML+                        1993
HTML 2.0                    1995
HTML 3.2                    1997
HTML 4.01                  1999
XHTML 1.0                  2000
HTML5                        2012
XHTML5                      2013

 The <!DOCTYPE> Declaration

 The <!DOCTYPE> declaration helps the browser to display a web page correctly.
There are many different documents on the web, and a browser can only display an HTML page 100% correctly if it knows the HTML type and version used.

 Common Declarations

 HTML5

 <!DOCTYPE html>

 HTML 4.01

 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">

 XHTML 1.0

 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

 For a complete list of document type declarations, go to our DOCTYPE Reference.

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run time polymorphism


runtime polymorphism in java :: futureX
Runtime polymorphism or dynamic method dispatch is a process in which a call to an overridden method is resolved at runtime rather than at compile-time.In this process, an overridden method is called through the reference variable of a superclass. The determination of the method to be called is based on the object being referred to by the reference variable.


 UPCASTING :
When reference variable of Parent class refers to the object of Child class, it is known as upcasting.
upcasing in java :: futureX
For example:


class Animal{
void eat(){System.out.println("eating food");}
}

 class Human extends Animal{
void eat(){System.out.println("eating delicious food");}

 public static void main(String args[]){
Animal A=new Human();
A.eat();
}
}

 Example of runtime polymorphism


class Bike{
   void run(){System.out.println("running");}
 }
 class Splender extends Bike{
   void run(){System.out.println("running safely with 60km");}

   public static void main(String args[]){
     Bike b = new Splender();//upcasting
     b.run();
   }
 }


In this example, we are creating two classes Bike and Splendar. Splendar class extends Bike class and overrides its run() method. We are calling the run method by the reference variable of Parent class. Since it refers to the subclass object and subclass method overrides the Parent class method, subclass method is invoked at runtime. Since it is determined by the compiler, which method will be invoked at runtime, so it is known as runtime polymorphism.
Rule: Runtime polymorphism can't be achieved by data members.

 class Bike{ int speedlimit=90; } class Honda extends Bike{ int speedlimit=150; public static void main(String args[]){ Bike obj=new Honda(); System.out.println(obj.speedlimit);//output 90 } }

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