Data Types In Java

Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory.
Based on the data type of a variable, the operating system allocates memory and decides what can be stored in the reserved memory
There are two data types available in Java:

1. Primitive Data Types
2. Reference/Object Data Types/User Define Data Types

The Primitive Data Types

Java defines eight primitive data  types of data :byte,short,int,long,char,float,double and boolean.The primitive types also commonly known as simple data types. Primitive data types are predefined by the language and named by a keyword.These can be put into four groups:

• Integers : This group includes byte,short,int and long which are for whole valued signed numbers.
• Floating-point numbers : This group includes float and double whic represent numbers with fractional precision.
• Characters : This group includes char, which represents symbols in character set.
• Boolean : This group includes boolean , which represents only true or false.

Integers :

Java defines four integer types  byte,short,int and long .All of these are signed , positive and negative values.Java dose not  support unsigned , positive integers. 

Name	Size	Range
byte	8	-128 to 127
short	16	-32,768 to 32,767
int	32	-2,147,483,648 to 2,147,483,647
long	64	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

byte:

• The smallest integer type.
• This is signed 8-bit  type.
• byte type variables are very useful when working with a stream of data from network or file.
• Default value is 0.
• byte variables are declared by byte keyword. E.g. byte b ,  here byte is datatype and b is variable name.

short:

• short is signed 16-bit type.
• It is least used java type.
• Default value is 0
• short variables are declared by short keyword. E.g short xyz , here short is data type and xyz is variable name.

int : 

• The most commonly used integer type is int.
• It is a signed 32-bit type.
• Default value is 0
• int variables are declared by int keyword. E.g. int xyz ,  here int is datatype and xyz is variable name.

long : 

• long is a signed 64-bit type.
• It is useful where an int type is not large enough to hold the desire value.
• Default value is 0L.
• long variables are declared by long keyword. E.g. long xyz ,  here long is datatype and xyz is variable name.

Floating-point Types:

Floating point numbers are also known as the real numbers,and used when evaluating expressions that returns fractional precision.

Name	Size	Range
float	32	1.4e-045 to 3.4e+038
double	64	4.9e-324 to 1.8e+308

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 variables are declared by float keyword. E.g. float xyz ,  here float is datatype and xyz is variable name.

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.
• Default value is 0.0d.
• double variables are declared by double keyword. E.g. double xyz ,  here double is datatype and xyz is variable name.

Char : 

• char data type is a single 16-bit Unicode character.
• Char data type is used to store any character.
• char variables are declared by char keyword. E.g. char xyz ,  here char is datatype and xyz is variable name.

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.
• boolean variables are declared by boolean keyword. E.g. boolean xyz ,  here boolean is datatype and xyz is variable name.

Reference/Object Data Types:

• Reference variables are created using defined constructors of the classes. They are used to access objects. These variables are declared to be of a specific type that cannot be changed. For example, Employee, Student,Test  etc.
• Class objects, and various type of array variables come under reference data type.
• Default value of any reference variable is null.
• A reference variable can be used to refer to any object of the declared type or any compatible type.
• E.g. Test t=new Test();