02. How To Write JAVA Programmes

1. Basic Java Program

Code :

// Hello world program in JAVA

class hello

{

public static void main(String args[]) // this is the main method

{

System.out.println("Hello World \n");

}

}

Preview : 

2. JAVA Translation

Java Translation Process 
Java Source Code -> (Java Compiler) -> Java Byte Code -> (Byte Code Interpreter) -> Machine Language -> output

Java Source Code : .java file
Java Byte Code    : .class file

3. Comments & Conventions

// - Single line comment
/*...*/ - block comment ( multiple lines )

• Java is case sensitive
  

Code :

public class secondFile

{

public static void main(String[] args)

{

System.out.print(" Java is a very portable language ");

System.out.println(" and can run in different tpes of computers. ");

System.out.println(" this is next line!!!! ");

}

}

Preview : 

4. Keywords

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

*		not used
**		added in 1.2
***		added in 1.4
****		added in 5.0

source for the keywords : http://download.oracle.com/javase/tutorial/java/nutsandbolts/_keywords.html

5. Identifiers 

Identifiers are Case senstive.

Names given for variables , classes and methods

VALID : employeeName, Emp_number, $Emp_salary

INVALID : employee name, #emp, class
"employeeName" method is called the camel method.


6. Data Types

Primitive Data Types:

Data Type	Default Value (for fields)
byte	0
short	0
int	0
long	0L
float	0.0f
double	0.0d
char	'\u0000'
String (or any object)	null
boolean	false

Source : http://download.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html

Refernce Data Types: 

Array
Class

Code :

public class tempConv

{

public static void main(String[] args)

{

float celsius = 100;

float fahrenheit ;

//convert to Fahrenheit equivalent

fahrenheit = 32 + ((9 * celsius) / 5 );

System.out.println("celsius temprature");

System.out.println("  " + celsius);

System.out.println("Equivalent Fahrenheit Temperature ");

System.out.println("  " + fahrenheit);

}

}

Preview :