Basics OF Java

It  is very important to keep in mind the basic syntax of java program.
Basic Syntax:

Case Sensitivity - Java is case sensitive, which means identifier Test and test would have different meaning in Java.

Class Names - Class names should be start with upper case letter.If several words are used to form a name of the class, each inner word's first letter should be in Upper Case.
E.g. class MyFirstJavaProgram

Method Names - All method names  should be start with a Lower Case letter.If several words are used to form the name of the method, then each inner word's first letter should be in Upper Case.
E.g public void myFirstMethod()

Source  File Name - Name of the program file should exactly match the class name.
When saving the file, you should save it using the class name  and append '.java' to the end of the name.If the file name and the class name do not match your program will not compile.
E.g. : Assume 'Test' is the class name. Then the file should be saved as 'Test.java'

public static void main(String args[]) - Java program execution  starts from the main() method which is a mandatory part of every Java program.The main() method should have public and static  access modifier,void return type and string array as argument.
If we supply return type other than void then program compile successfully but it's not execute.

Java Identifiers:
All Java components require names. Names used for classes, variables and methods are called identifiers.
In Java, there are several points to remember about identifiers. They are as follows:
1. All identifiers should contains only character(A to Z or a to z),digit (0 to 9) and ( $ , _ ).
2. All identifiers should begin with a letter (A to Z or a to z), dollor character ($) or an underscore ( _ ).
3. After the first character identifiers can have any combination of characters,digits and ($) ,( _ ).
4. A key word cannot be used as an identifier.
5. Identifiers are case sensitive.

Example of identifiers
Legal identifiers: age, $salary,  _value , __1_value , abc123,abc_ xyz
Illegal identifiers: 123abc, -salary,@abc,abc!,abc@xyz

Java Modifiers:
There are two types of modifiers in java:
1. Access Modifiers: default, public , protected, private
2. Non-access Modifiers: final, abstract, strictfp,transient,native .
We will see into more details about modifiers in other post.

Java Variables:
We would see following type of variables in Java:
1.Local Variables
2.Class Variables (Static Variables)
3.Instance Variables (Non-static variables)

Class and Instance variables are global variables.

Java Keywords:

The following list shows the reserved words in Java. These reserved words may not be used as constant or variable or any other identifier names.

abstract	assert	byte	boolean
break	case	catch	char
class	const	continue	default
do	double	else	enum
extends	final	finally	float
for	goto	if	implements
import	instanceof	int	interface
long	native	new	package
private	protected	public	return
short	static	strictfp	super
switch	synchronized	this	throw
throws	transient	try	void
volatile	while

Comments in Java:

Java supports single-line and multi-line comments . All statements  available inside any comment are ignored by Java compiler.

public class Test


{

  public static void main(String []args)

  {
    // This is an example of single line comment

    /* This is also an example of multi line comment.
       This is also an example of multi line comment.
       This is also an example of multi line comment
       This is also an example of multi line comment */



       System.out.println("Hello Collegeone users !");
  }

}