Data Types in Java

Java language has a rich implementation of data types. Data types specify size and the type of values that can be stored in an identifier.

In java, data types are classified into two catagories :

  1. Primitive Data type
  2. Non-Primitive Data type

1) Primitive Data type

A primitive data type can be of eight types :

Primitive Data types
charbooleanbyte shortintlongfloat double

Once a primitive data type has been declared its type can never change, although in most cases its value can change. These eight primitive type can be put into four groups


Integer

This group includes byte, short, int, long

byte : It is 1 byte(8-bits) integer data type. Value range from -128 to 127. Default value zero. example: byte b=10;

short : It is 2 bytes(16-bits) integer data type. Value range from -32768 to 32767. Default value zero. example: short s=11;

int : It is 4 bytes(32-bits) integer data type. Value range from -2147483648 to 2147483647. Default value zero. example: int i=10;

long : It is 8 bytes(64-bits) integer data type. Value range from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807. Default value zero. example: long l=100012;


Floating-Point Number

This group includes float, double

float : It is 4 bytes(32-bits) float data type. Default value 0.0f. example: float ff=10.3f;

double : It is 8 bytes(64-bits) float data type. Default value 0.0d. example: double db=11.123;


Characters

This group represent char, which represent symbols in a character set, like letters and numbers.

char : It is 2 bytes(16-bits) unsigned unicode character. Range 0 to 65,535. example: char c='a';


Boolean

This group represent boolean, which is a special type for representing true/false values. They are defined constant of the language. example: boolean b=true;


2) Non-Primitive(Reference) Data type

A reference data type is used to refer to an object. A reference variable is declare to be of specific and that type can never be change. We will talk a lot more about reference data type later in Classes and Object lesson.


Identifiers in Java

All Java components require names. Name used for classes, methods, interfaces and variables are called Identifier. Identifier must follow some rules. Here are the rules:

  • All identifiers must start with either a letter( a to z or A to Z ) or currency character($) or an underscore.
  • After the first character, an identifier can have any combination of characters.
  • A Java keyword cannot be used as an identifier.
  • Identifiers in Java are case sensitive, foo and Foo are two different identifiers.