Java Tutorial

Java is a general purpose, high-level programming language developed by Sun Microsystems. 

Java is an object-oriented language similar to C++, but simplified to eliminate language features that cause common programming errors.

Where it is used?

According to Sun, 3 billion devices run java. There are many devices where java is currently used. Some of them are as follows:

1. Desktop Applications such as acrobat reader, media player, antivirus etc.

2. Web Applications such as irctc.co.in, javatpoint.com etc.

3. Enterprise Applications such as banking applications.

4. Mobile

5. Embedded System

6. Smart Card

7. Robotics

8. Games etc.

Types of Java Applications

There are mainly 4 type of applications that can be created using java programming:

1) Standalone Application

It is also known as desktop application or window-based application. An application that we need to install on every machine such as media player, antivirus etc. AWT and Swing are used in java for creating standalone applications

.

2) Web Application

An application that runs on the server side and creates dynamic page, is called web application. Currently, servlet, jsp, struts, jsf etc. technologies are used for creating web applications in java.

3) Enterprise Application

An application that is distributed in nature, such as banking applications etc. It has the advantage of high level security, load balancing and clustering. In java, EJB is used for creating enterprise applications.

4) Mobile Application

An application that is created for mobile devices. Currently Android and Java ME are used for creating mobile applications.

Stream

A stream is a sequence of data.In Java a stream is composed of bytes. It's called a stream because it's like a stream of water that continues to flow.

In java, 3 streams are created for us automatically. All these streams are attached with console.

1) System.out: standard output stream

2) System.in: standard input stream

3) System.err: standard error stream

Let's see the code to print output and error message to the console.

System.out.println("simple message");  

System.err.println("error message");  

Let's see the code to get input from console.

int i=System.in.read();//returns ASCII code of 1st character  

System.out.println((char)i);//will print the character  

Data Types in Java

In java, there are two types of data types primitive data types non-primitive data types

Data Type	Default Value	Default size
boolean	false	1 bit
char	'\u0000'	2 byte
byte	0	1 byte
short	0	2 byte
int	0	4 byte
long	0L	8 byte
float	0.0f	4 byte
double	0.0d	8 byte

Types of Variable

There are three types of variables in java local variable instance variable static variable

Local Variable

A variable that is declared inside the method is called local variable.

Instance Variable

A variable that is declared inside the class but outside the method is called instance variable . It is not declared as static.

Static variable

A variable that is declared as static is called static variable. It cannot be local.

class A{  

int data=50;//instance variable  

static int m=100;//static variable  

void method(){  

int n=90;//local variable  

}  

}//end of class  

Operators in java

Operator in java is a symbol that is used to perform operations. There are many types of operators in java such as unary operator, arithmetic operator, relational operator, shift operator, bitwise operator, ternary operator and assignment operator.

Operators	Precedence
postfix	expr++ expr--
unary	++expr --expr +expr -expr ~ !
multiplicative	* / %
additive	+ -
shift	<< >> >>>
relational	< > <= >= instanceof
equality	== !=
bitwise AND	&
bitwise exclusive OR	^
bitwise inclusive OR	|
logical AND	&&
logical OR	||
ternary	? :
assignment	= += -= *= /= %= &= ^= |= <<= >>= >>>=

Loop

Java programming language provides the following types of loop to handle looping requirements. Click the following links to check their detail.

Loop Type	Description
While loop	Repeats a statement or group of statements while a given condition is true. It tests the condition before executing the loop body.
For loop	Execute a sequence of statements multiple times and abbreviates the code that manages the loop variable.
Do..while loop	Like a while statement, except that it tests the condition at the end of the loop body

While loop

For loop

Do…while loop

Decision making statement

Java programming language provides following types of decision making statements. Click the following links to check their detail.

Statement	Description
If statement	An if statement consists of a boolean expression followed by one or more statements.
If..else statement	An if statement can be followed by an optional else statement, which executes when the boolean expression is false.
Nested if statement	You can use one if or else if statement inside another if or else if statement(s).
Switch statement	A switch statement allows a variable to be tested for equality against a list of values.

If statement

If…else statement

If...elseif statement

Switch statement

Java - Arrays

Java provides a data structure, the array, which stores a fixed-size sequential collection of elements of the same type.

Declaring Array Variables

dataType[] arrayRefVar;   // preferred way.

or

dataType arrayRefVar[];  //  works but not preferred way.

Java String class methods

The java.lang.String class provides many useful methods to perform operations on sequence of char values.

No.	Method	Description
1	char charAt(int index)	returns char value for the particular index
2	int length()	returns string length
3	String substring(int beginIndex)	returns substring for given begin index
4	static String join(CharSequence delimiter, CharSequence... elements)	returns a joined string
5	boolean equals(Object another)	checks the equality of string with object
6	boolean isEmpty()	checks if string is empty
7	String concat(String str)	concatinates specified string
8	String trim()	returns trimmed string omitting leading and trailing spaces
9	String split(String regex)	returns splitted string matching regex
10	String split(String regex, int limit)	returns splitted string matching regex and limit
11	int indexOf(int ch)	returns specified char value index
12	int indexOf(int ch, int fromIndex)	returns specified char value index starting with given index
13	String toLowerCase()	returns string in lowercase.
14	String toUpperCase()	returns string in uppercase.

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