The document provides an overview of variables and data types in Java, including definitions and examples of primitive, reference, and user-defined data types. It explains the memory storage of variables, their declaration, and includes sample programs demonstrating basic operations like sum and division. Additionally, it discusses naming conventions, reserved keywords, and common Java syntax for documentation and comments.

1. Programming in Java
Variable & Data Types
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2. Variable
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name
• Store any type of Value or Data.
• A specific name of Memory region.
• Data type will decide what values will be stored in
variables.
• You can say data type will define the structure of
your data
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3. Data type
a b
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int String
Water- (Value)
Liquid- (Type)
Bottle- (Variable)
• Define the data structure
• Identify type of value/data
Ram
int float
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4. Categories of data type
• Primitive Data type
• Reference Data type/Composite data type
• User Define/Custom Data type
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5. boolean – 1 byte
1. Primitive Data type
Primitive (8)
Numeric (6) Non-Numeric (2)
Integral (4) Floating (2)
char – 2 byte
(Unicode)
float - 4 byte
double – 8 byte
byte - 1 byte
short - 2byte
int - 4byte
long – 8 byte
• It stores value.
• It occupies number of bytes as per data type.
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6. Primitive Data types
• Decimal values will be stored in float and double
data type.
• Non-decimals values will be stored in int, long,
byte and short data types.
• Character will be stored in char data type.
• true/false will be stored in boolean data types.
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7. Primitive Data type detail
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8. 2. Reference/Composite Data
type
Reference/Composite Data
type (3)
String
• It stores memory address of a value.
• It occupies 2 bytes to store a reference (Memory Address).
Array
Object
Ex.
String name = “infovia”
name variable store total size of
value is
address of value “infovia” 14 byte, 2 byte
per it occupies 2
byte. character
i n f ao v i
2 2 2 2 2 2 2
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9. 3. User Defined/Custom data type
User Defined/Custom (2)
• It contains multiple member and member method.
• Size depends on content
class Name {
String firstName;
String middleName;
String lastName;
void printFullName() {
----
}
}
class
enum
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10. Program - Sum of two numbers
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public class Sum {
public static void main(String[] args) {
int firstValue, secondValue, resultOfSum;
firstValue = 25;
secondValue = 15;
resultOfSum = firstValue + secondValue ;
System.out.println(“Sum Result is = ”+ resultOfSum);
}
}
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11. Variable declaration
type variable_name;
Meaning: variable <variable-name> will be a variable of type
<type>
Where type can be:
int //integer
double //real number
Example:
int a, b, c;
double x;
int sum;
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12. Types of Variable ?
Instance/global
Static
local
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13. Program - Division
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public class Division {
public static void main(String[] args) {
float a, b, c;
a = 25.678f;
b = 15;
c = a / b;
System.out.println(“Division Result is = ”+ c);
}
}
/* Output
Division Result is = 1.7118666
if use double data type then result is =
1.7118666330973307
*/
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14. Program - DataTypeExercise
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public class DataTypeExercise {
public static void main(String[] args) {
int i =50;
float f = 25.5f;
double d = 89.789;
boolean b = true;
System.out.print(“ ”+ i + b + f + d)
;
}
}
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15. Constant declaration
Declare variable -
syntax =
type variable_name;
ex. –
double radius = 2.45; // it can be change
Declare Constant -
syntax =
final type constant_name= value;
ex. –
final double PI = 3.1415; // can not be change, now it
fixed
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16. Program –Constant Area of
Circle
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public class AreaOfCircle {
public static void main(String[] args) {
final double PI = 3.1415;
double area;
float radius = 3.5f ;
area = PI* radius * radius ;
System.out.println(“Area of Circle = ”+
area);
}
}
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17. Java Comments
• Single-line comment – it is used to comment only one
line.
• Multi-line comment - it is used to comment multiple
lines of code.
• Document comment – it is used to create documentation
API.
Example :
Single Line Comment –
//This is single line comment
Multi Line Comment
/* This is Multi Line Comment
this is multi line comment */
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18. Identifier
• A name in java program is identifier, which can be
used for identification purpose.
• It can be method name, variable name, class name or
label name.
public class Test{
public static void main(String[] args){
int x = 25;
}
}
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19. Naming convention rules
Rules of defining name (identifier) –
Can use – a to z A to Z 0 to 9 $ _
Identifier -
total_number ok //correct
total# no //can not use symbol
total123 ok //correct
123total no //can not starts with digit
if no //reserve word
ca$h ok //can use, no error, but use at special
case
_$_$_$_$_ ok //can use, no error
all@hands no //can not use symbol
Java2Share ok //correct
Interger ok //can use, no error, but not use because it is
prefined class
Int ok //can use, no error 19
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20. Naming convention rules
class Test{
public static void main(String args[]) {
int number = 10;
int Number = 20; //ok, but use with class (first
character of class name is capital)
int NUMBER =30; //ok, but use with Constant
declaration(All Caps)
int String =78; // ok, no error, but - wrong it is
predefine class
int Runnable = 78; // ok, no error, but - wrong predefine
Interface
} // we can differentiate
with case
} //case sensitive programming
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21. Java Reserved words
• All are written in small letters
false
Reserved
words(53)
Keyword (50)
Reserved literal
(3)
Used (48) Un-used (2) true
goto
const
if, else, for….. Etc.
null
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22. Return type keyword (1) - void
Used Keywords - 48
Keyword for data type (8) - byte, short, int, long, float, double, char,
boolean
Keyword for control statements (11) –
if, else, switch, case, default, while, do, for, break, continue , return
Keyword for exception handling(6) - try, catch, finally, throw, throws, assert
(1.4)
Keywords for access modifier (11) -
private, public, protected, static , final, abstract, synchronized, native,
strictfp (1.2), transient, volatile
Class related keywords (6) - class, interface, extends, implements, package,
import
Object related keywords(4) - new, instanceof, super, this
To define group of named constants (1) – enum (1.5)
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23. Literals
int x = 20;
[Data typevariable constant | literal ]
int x= 10; //decimal value
int x= 010; //octal value -> 8 (octal to
decimal)
int x= 0X10; //hexadecimal value-(base -16)
int x = 10; //ok
int x = 0788; // no CE
int x = 0777 // ok
int x = 0XFace; // ok
int x= 0XBeef; //ok
int x = 0XBeer; //no
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24. Type Specifier
n new line
t horizontal tab
r carriage return
b back space
f form feed
’ single quote
” double quote
back slash
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25. QA
1. Is Java primitive data type stored on stack or heap?
2.What is the default value of local variables in Java?
3.Can you compare a boolean with an int variable in
Java?
4.What is the default value of char data type in Java?
5.What is the output?
System.out.println(1.0/0);
6.Which format is used for char data type in java?
7. Difference between primitive variables and reference
variables?
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26. Get in Touch
Thank You
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