Interrogation Of First JAVA Program

Class FirstJavaProgram
{
      public static void main (String [] args)
     {
               System.out.println("Hello World!");
      } // main
} // class


In Java Program EveryThing is a CLASS.

1- First we write class and class_name
2- main() method
3- method/function to display something to the screen

--> These three steps are needed to follow for understanding & execution of the program.

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# Syntax Of CLASS

Accessibility_Modifier are -

• public
• private
• protected

Modifiers are - 

• final
• static
• abstract
• many more (Will see all of them later)

class - class is a keyword. It should be written as it is. [all the keyword are written in small letters in java ]

Class_Name - Here "FirstJavaProgram"  is a name of the class.


******************************************************

Now, Main() Method

*This Is Very Important (It may chance to asks question on this in an interview room)
we will see this later when you are in a position to understand these concepts.
As of now I just introduce these words to you.

[Note - by heart this line (without this line you cannot run any program in java)]

public - is an access modifier.

static - is a keyword.

void - it is a DATA TYPE.

main() -

• it is the name of main() a method. 
• JVM is always looking for the main() method.
• it is the parametrized method, it takes one argument of string type of array.
• You can't change its name, if you want to do so - for that you have to customize your JVM and it is almost impossible. 

String [] args - String is a class in java and args is the name of string type array.


As of now, it is enough but still, you want to know more about " public static void main(Strings [] args) "

Then I am going to give you video link - that will help you to understand this line clearly.

 [ Video -public static void main(Strings [] args) == 1st part ]

 [ Video -public static void main(Strings [] args) == 2nd part ]

 [ Video -public static void main(Strings [] args) == 3rd part ]

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Now, Output Stream

System.out.println(); - helps to display something on the screen.

System - is a class. (I told you before every thing in java is a class)

out - is a static variable.

println() - is a method of System Class.  

As of now, it is enough but still you want to know more about System.out.println();
Then i am going to give you video link - that will help you to understand this line clearly.

[ Video - Explanation about System.out.println(); ]

******************************************************

Now, Comments 

• Comments are something that is unreadable in java.
• it is used to increase the readability of the program.
• Java Compile ignores it.
• Two Types of Comment in Java
• Single Line Comment
• Multiple Line Comment
• Documentation Comment

// double forward slash used for single line comment

/*

* this is used 

* for multi-line comment, 

* what every written inside these (  /*  _comment_   */  )  is never

* executed at all.

*/

/**
*  it appears in blue color
*  this comment is for other developers
* These comments have some "@" words
*  used for -- last modification date, developed by, modified by etc
*/