Variables and Data Types in java

Variable is name of memory location. In java there are three types of variables instance variables, local variables, static variables.

There are two types of data types in java

1) Primitive data types.
2) Non-Primitive data types.

Variable

Variable is name of reserved area allocated in memory. In other words, is name of memory location.

For example:

(1) int v = 20;   

Here v is a variable, Which holds the value 20..

(2) double d = 30;

Here d is a variable, Which holds the value 30.

Variable declaration

• int a;
• int a, b, c;

Variable initialization

• int a = 10;
• int a = 10, b = 20, c = 30.

Types of Variable

There are three types of variables in java:

1. Instance Variable.
2. Local Variable.
3. Static Variable.

Instance Variable

Instance variable is a variable , which is declared inside a class but outside of method is called instance variable. Instance variable gets memory at run time when object is created.

Local Variable

Local variable is a variable , which is declared inside of method is called local variable.

Static Variable

Static variable is a variable , which is defined by the static keyword is known as static variable. static variable cannot be local variable. Static variable belongs to class level variable.

Let's see the example in program

class TypesOfVariableExample

{

int a=10; //instance variable

static int b=20; //static variable

void show()//method declaration

{

int c=30; //local variable

}

}

We can define a variable in two location in a class. For example

class Demo

{

int a;//class level variables

int b;//class level variables

public static void main(String args[])

{

int c;//Local variables

int d;//Local variables

}

}

Data Types In Java

Data Types: data types represent the different  values to be stored in the variable. In java there are two types of data types.

(1) Primitive data type.
(2) Non-Primitive data type.

Primitive Data Type

(1) byte - 

Default  Size - 1 Byte
Default  Value - 0
Range : -128 to 127

For Example:

byte b=10;

(2) short -

Default  Size - 2 Byte
Default  Value- 0
Range : -32768 to 32767 

For Example:

short s=10;

(3) int - 

Default  Size - 4 Byte
Default  Value- 0
Range : -2147483648 to 2147483647

For Example:

int i=10;

(4) long - 

Default  Size - 8 Byte
Default  Value- 0L
Range : -9223372036854775808 to 9223372036854775807

For Example:

long l=10;

(5) char -

Default  Size - 2 Byte
Default  Value- '\u0000'
Range : 0 to 65536 (Unsigned) 

For Example:

char c='a';

(6) boolean -

Default  Size - 1 bit
Default  Value- false
Range : true/false

For Example:

boolean b=true or false;

(7) float -

Default Size - 4 Byte
Default Value - 0.0f
Range :  approximately (+-) 3.40282347E+38F(6-7 significant decimal digits) Java implements IEEE 754 standard

For example :

float f=2.3f;

(8) double -

Default Size - 8 Byte
Default Value - 0.0d
Range :  approximately (+-) 1.79769313486231570E+308(15 significant decimal digits)

For example :

double d=8.5d;

Note:There is 1 byte=8 bit;

Non-Primitive or reference or object Data types

• String
• Array
• Enumeration
• etc

What is signed and unsigned in java 

Signed(+ or -): signed data types can hold both positive and negative values.

Unsigned(+): unsigned data types can hold large positive values but can't hold negative values.

For example:

A signed byte can represent values -128 to 127, while an unsigned byte can represent values from  0 to 255.

👉: In java all the data types or data types values are signed(except char)