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. Therefore, by assigning different data types to variables, you
can store integers, decimals, or characters in these variables.
There are two data types available in
Java:
Primitive Data Types
Reference/Object Data Types
There are eight primitive data types
supported by Java. Primitive data types are predefined by the language and
named by a keyword. Let us now look into detail about the eight primitive data
types.
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
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
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 a = 100000, int b = -200000
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 = 100000L, int b =
-200000L
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 f1 = 234.5f
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 d1 = 123.4
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
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'
Reference 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, Puppy 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.
Example: Animal animal = new
Animal("giraffe");
Java Literals:
A literal is a source code
representation of a fixed value. They are represented directly in the code
without any computation.
Literals can be assigned to any
primitive type variable. For example:
byte a = 68;
char a = 'A'
byte, int, long, and short can be
expressed in decimal(base 10), hexadecimal(base 16) or octal(base 8) number
systems as well.
Prefix 0 is used to indicate octal and
prefix 0x indicates hexadecimal when using these number systems for literals.
For example:
int decimal = 100;
int octal = 0144;
int hexa = 0x64;
String literals in Java are specified
like they are in most other languages by enclosing a sequence of characters
between a pair of double quotes. Examples of string literals are:
"Hello World"
"two\nlines"
"\"This is in
quotes\""
String and char types of literals can
contain any Unicode characters. For example:
char a = '\u0001';
String a = "\u0001";
Java language supports few special
escape sequences for String and char literals as well. They are:
Notation Character
represented
\n Newline
(0x0a)
\r Carriage
return (0x0d)
\f Formfeed
(0x0c)
\b Backspace
(0x08)
\s Space
(0x20)
\t tab
\" Double
quote
\' Single
quote
\\ backslash
\ddd Octal
character (ddd)
\uxxxx Hexadecimal UNICODE charac
