Java Variable And Data Type - Androidpro

 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, 8989.98f,  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.

 

 

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