Free WebSchools.com

HOME

J2ee tutorials

Java introduction
Java basic
Java installation
Java Packages
Learn Applets
Java Threads
Java Gui component

Java Event Handaling
Java Streams and Files

Java Swings
Java JDBC

Java Network Programming
Java RMI

Java Servlets
Java javabeans

EJB
Struts

Writing first java program

public class first
{
public static void main(String str[])
{
System.out.println("this is my first java program");
}
}

The output of the above example is

this is my first java program.

how to run the program?

I will explain how to run thE program step by step.

step 1 create a new folder called myprogram and save the first.java(the file name same as class name) on that folder.

step 2 complile the program using javac.exe file.type the following program in the command prompt

c:\myprogram>javac first.java

step 3 to run the program type the following command on the command prompt c:\>java first
thats it this is your first java program congrates!!!!!!!!!!!

comments:

comments are statements which are ignored by compiler

/* this is an example of mulitple line comment */

single line comment
// this is single line comment

identifiers

identifiers are the name given to variable,methods,classes,packages and interfaces.
the following are the valid variable .
myvariable
Myvariable
MYVARIABLE
_MYVA
x

Java keywords

Keywords are reserved words that are predefined by the language and cannot be used as identifier. Keywords are reserved for their intended use and cannot be used by the programmer for variable or method names. Keywords are listed below

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

data types in java

data types in java are categorized into two parts

primitive data type
Reference data type

In java you will be using 8 data types called PRIMITIVE DATA TYPES.These are 8 types are byte,short,int,long,char,float,double and boolean.

Java Operators

OPERATORS ARE THE SYMBOL THAT MAKES IT POSSIBLE TO USE ON fOR MORE VALUES TO PRODUCE A NEW VALUE. A VALUE THAT IS OPERATED ON BY AN OPERATOR IS AN OPEREND.

Different operators used in Java.

Arithmetic Operators

Operator	Description	Example	Result
+	Addition	x=2 x+2	4
-	Subtraction	x=2 5-x	3
*	Multiplication	x=4 x*5	20
/	Division	15/5 5/2	3 2.5
%	Modulus (division remainder)	5%2 10%8 10%2	1 2 0
++	Increment	x=5 x++	x=6
--	Decrement	x=5 x--	x=4

Assignment Operators

Operator	Example	Is The Same As
=	x=y	x=y
+=	x+=y	x=x+y
-=	x-=y	x=x-y
*=	x*=y	x=x*y
/=	x/=y	x=x/y
%=	x%=y	x=x%y

Comparison Operators

Operator	Description	Example
==	is equal to	5==8 returns false
!=	is not equal	5!=8 returns true
>	is greater than	5>8 returns false
<	is less than	5<8 returns true
>=	is greater than or equal to	5>=8 returns false
<=	is less than or equal to	5<=8 returns true

Logical Operators

Operator	Description	Example
&&	and	x=6 y=3 (x < 10 && y > 1) returns true
\|\|	or	x=6 y=3 (x==5 \|\| y==5) returns false
!	not	x=6 y=3 !(x==y) returns true

conditional statement

conditional statements allow execution of selected statements or portion of the program,based on the value of some expressions.

if statement

Almost all computer programs need to make decisions. They test a condition and operate differently based on the outcome of the test. All programming language have some form of an if statements that tests conditions. The basic syntax of if statement is

If (Boolean expression)
Statement or block

the arguments to a conditional statement like if must be a boolean value consider the example

class ifexample
{
public static void main (String args[])
{
int a=9;
int b=8;
if(a>b)
{
System.out.println("a is greater than b");
}
}

The output will be as follows
a is greater than b

if else statement

if(a>b)
System.out.println("a is greater than b");
else System.out.println("b is greater than a");

switch statement

switch statements are shortened for certain kinds of if statements.the example is as follows

switch(x)
{
case 0:do something;
break;
case 1: do something;
break;
case 2: do something;
break;
case 3: do something;
break;
default: do something else;
}

Looping Statement

There might be a situation where you want to execute a statement or a block repeatedly. Take a simple example; you want to display integers starting 1 to 10. You can simply write 10 println statements as given below

System.out.println(1);
System.out.println(2);
System.out.println(3);
System.out.println(4);
System.out.println(5);
System.out.println(6);
System.out.println(7);
System.out.println(8);
System.out.println(9);
System.out.println(10);

But imagine if you want to display numbers form 1 to 100 or 1000. For this you need loops or looping statements. Following are the looping statement used in java.

while Statement

general syntax of the while loop is

while (boolean condition)
statement or block

consider the example

public class stars
{
public static void main(String [] s)
{
int a=1;
while(a<10)
{
System.out.println(a);
a++;
}
}
}