Java Variable
Variable in Java is a data container that
stores the data values during Java program execution. Variable is a memory
location name of the data. . Every variable is assigned data type which
designates the type and quantity of value it can hold. The Java variables have three types of variables - local, instance and static.
To indicate the storage area,
each variable should be given a unique name (identifier).
1. Variable Declaration
2. Variable Initialization
Variables Declaration in Java
Here's how we create a variable in Java, To declare a variable, you
must specify the data type & give the variable a unique name.
Examples of other Valid Declarations
are
int var ;
float floatvar;
double doublevar;
Note – int , float , double
are data types and after that var, floatvar , doublevar
are variable name you can put any others name as you want according data types
:
Variable
Variable is name of reserved area allocated in memory. In other words, it
is a name of memory location. It is a combination of "vary + able"
that means its value can be changed.
Variable Initialization:
To initialize a
variable, you must assign it a valid value.
Example of other
Valid Initializations are
var = 89;
floatvar = 89.98f;
doublevar = 76.9;
You can combine
variable declaration and initialization.
int var = 89;
float floatvar = 89.98f;
double doublevar = 76.9;
Change values of variables
The value of a variable can be changed in the program, hence the name variable.
For example,
//
before
int var = 89;
float floatvar = 89.98f;
double doublevar = 76.9;
// after
int var = 898;
float floatvar = 879.98f;
double doublevar = 976.9;
Rules for Naming Variables in Java
Java programming language has its own set of rules
and conventions for naming variables. Here's what you need to know:
Java is case sensitive.
Hence, age and AGE are two different variables. For example,
int age = 8;
int Age = 87;
Variables must start with
either a letter or an underscore, _ or
a dollar, $ sign. For example,
int Age = 8;
int _Age = 87;
int $Age = 87;
Variable names cannot start
with numbers. For example,
int 1Age = 8;
Variable names can't use whitespace.
For example,
int _Age Rahul = 87;
There are types of variables in Java programming language:
- Instance Variables
(Non-Static Fields)
- Class Variables (Static
Fields)
- Local Variables
- Parameters
1) Local Variables
Local Variables are a variable that are declared inside
the body of a method. A local variable declared inside the body of the method
is called local variable. You can use this variable only within that method and
the other methods in the class aren't even aware that the variable exists.
A local variable cannot be
defined with "static" keyword
2) Instance Variables
A variable declared inside the class but outside the body
of the method, is called instance variable. It is not declared as static.
It is called instance variable because its value is
instance specific and is not shared among instances.
3) Static Variables
Static variables are initialized only once, at the start
of the program execution. These variables should be initialized first, before
the initialization of any instance variables.
Example: Types of Variables in Java
static int ab = 91; //static
variable
int intiger = 7; //instance
variable
void method() {
int a = 9; //local
variable
Java literals
Literals are data used for representing values.
They can be used directly in the code. For example,
int var = 89;
float floatvar = 89.98f;
Here, 89, 89.98f, are literals.
Here are different types of literals in Java.
1. Boolean Literals
In Java, boolean literals are used to initialize
boolean data types. They can store two values: true and false. For example,
boolean holiday = false;
boolean holiday = true;
2. Integer Literals
An integer literal is a numeric value. There are 4 types of integer
literals in Java:
1. binary (base 2)
2. decimal (base 10)
3. octal (base 8)
4. hexadecimal (base 16)
For example:
// binary Number
int binaryNumber = 0b110;
//
octal Number
int OctalNumber = 027;
//
decimal Number
int DecNumber = 34;
//
hexadecimal Number
int HexNumber = 0x2Fsd3; // 0x represents
hexadecimal
// binary
int BinNumber = 0b010; // 0b represents
binary
In Java, binary starts with 0b, octal starts with 0,
and hexadecimal starts with 0x.
3. Floating-point Literals
A floating-point literal is a numeric. For example,
float $Age = 87.6f;
double doublevar = 976.9;
4. Character Literals
Character literals are unicode character enclosed inside single quotes. For
example,
char A = 'a';
5. String literals
A string literal is a sequence of characters
enclosed inside double-quotes. For example,
String var = "Programming";
String va2 = "androidpro.in";
Here, Programming and androidpro.in are two string literals.
What is Data Types in Java?
The term data type refers to the type of data that can be stored in a
variable.
Sometimes, Java is called a “strongly typed language” because when you declare
a variable, you must specify the variable’s type.
Java has a rich set of data types. Data types in Java can be divided into
two parts :
1. Primitive Data Types :- which include
integer, character, boolean, and float
2. Non-primitive Data Types :- which include
classes, arrays and interfaces.
Primitive Data Types
Primitive Data
Types are predefined and available within the Java language. Primitive values
do not share state with other primitive values.
There are 8
primitive types: byte, short, int, long, char, float, double, and Boolean.
Integer data types
·
byte (1 byte)
·
short (2 bytes)
·
int (4 bytes)
·
long (8 bytes)
1. byte:
Byte data type is an 8-bit signed two's complement integer.
Minimum value is -128 (-2^7)
Maximum value is 127 (inclusive)(2^7 -1)
Default value is 0
Byte data type is used to save space in large arrays, mainly in place of
integers, since a byte is four times smaller than an int.
Example: byte a = 100 , byte b = -50
2. short:
Short data type is a 16-bit signed two's complement integer.
Minimum value is -32,768 (-2^15)
Maximum value is 32,767 (inclusive) (2^15 -1)
Short data type can also be used to save memory as byte data type. A short is 2
times smaller than an int
Default value is 0.
Example: short s = 10000, short r = -20000
3. int:
Int data type is a 32-bit signed two's complement integer.
Minimum value is - 2,147,483,648.(-2^31)
Maximum value is 2,147,483,647(inclusive).(2^31 -1)
Int is generally used as the default data type for integral values unless there
is a concern about memory.
The default value is 0.
Example: int ab = 10000, int bc = -20000
4. long:
Long data type is a 64-bit signed two's complement
integer.
Minimum value is -9,223,372,036,854,775,808.(-2^63)
Maximum value is 9,223,372,036,854,775,807 (inclusive). (2^63 -1)
This type is used when a wider range than int is needed.
Default value is 0L.
Example: long a = 1000L, int b = -2000L
Floating Data Type
· float (4 bytes)
·
double (8 bytes)
5. float:
Float data type is a
single-precision 32-bit IEEE 754 floating point.
Float is mainly used to save memory in large arrays of floating point numbers.
Default value is 0.0f.
Float data type is never used for precise values such as currency.
Example: float fa1 = a234.5f
6. double:
double data type is a
double-precision 64-bit IEEE 754 floating point.
This data type is generally used as the default data type for decimal values,
generally the default choice.
Double data type should never be used for precise values such as currency.
Default value is 0.0d.
Example: double dz1 = 1233.4
Textual Data Type
char (2 bytes)
7. char:
char data type is a single
16-bit Unicode character.
Minimum value is '\u0000' (or 0).
Maximum value is '\uffff' (or 65,535 inclusive).
Char data type is used to store any character.
Example: char letterA ='A'
Logical
boolean (1 byte)
(true/false)
8. boolean:
boolean data type represents one bit of
information.
There are only two possible values: true and false.
This data type is used for simple flags that track true/false conditions.
Default value is false.
Example: boolean one = true
|
Java Data
Types |
||
|
Data Type |
Default Value |
Default size |
|
byte |
0 |
1 byte |
|
short |
0 |
2 bytes |
|
int |
0 |
4 bytes |
|
long |
0L |
8 bytes |
|
float |
0.0f |
4 bytes |
|
double |
0.0d |
8 bytes |
|
boolean |
false |
1 bit |
|
char |
‘\u0000’ |
2 bytes |
Points to
Remember:
- All numeric data types
are signed(+/-).
- The size of data types
remain the same on all platforms (standardized)
· char data type in Java is 2
bytes because it uses UNICODE character set.
