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Datatypes ​

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4 min

Default values of datatypes ​

shell
 double : 0.0
 float : 0.0 / 0.0F 
 long : 0 / 0L
 int : 0
 short : 0
 char : '\u0000' (null character)
 byte : 0
 boolean : false
 String : null
 Object : null

ASCII

'A' = 65 'a' = 97

Important

Never use '' ( two apostrophe without space in between ) for assigning empty value to a char variable, instead use ' ' ( two apostrophe with space between ) or '\u0000'

char c = '';

error: empty character literal

Valid initializations :

char c = ' ';

char c = '\u0000';

Suffix

  • The suffix 'l' or 'L' when used after an integer signifies long value

Example :

java
long phoneNumber = 0000000000L;

TIP

Use long datatype for accepting large numbers like phone number from user because using int might cause an overflow

  • The suffix 'f' or 'F' when used after an floating point integer signifies float value

Example :

java
float pi = 3.14F;

TIP

Always try to use double instead of float to avoid confusion

Hierarchy of datatypes ​

shell
double
float  
long
int 
short
char
byte
boolean

NOTE

Although boolean datatype has the lowest precedence, we cannot upcast it to other numeric datatype like byte, char, int, etc

Yes, char is a numeric datatype. It is a 16-bit unsigned integer that stores the Unicode value of a character, ranging from 0 to 65,535

Therefore, char is the only unsigned primitive data type in Java (supports only positive numeric values)

TIP

To calculate Range of a integer datatype of n bits use the formula : -2ⁿ⁻¹ to 2ⁿ⁻¹ - 1

Reason : In binary system or Base₂ number system, n bits can store a maximum decimal / Base₁₀ number of 2ⁿ.(positive numbers only) but Java doesn't support unsigned datatypes.(i.e. only positive numbers; except for char). So to store equal number of positive and negative numbers in a variable, the range is reduced by half and becomes -2ⁿ⁻¹ to 2ⁿ⁻¹ - 1

NOTE

We have to subtract 1 from range in the last (2ⁿ⁻¹) so that we can include 0 in the range Range = 2ⁿ⁻¹ negative numbers + 0 + 2ⁿ⁻¹ - 1 positive numbers

Sizes of datatypes ​

shell
double  : 64 bits / 8 bytes
float   : 32 bits / 4 bytes
long    : 64 bits / 8 bytes
int     : 32 bits / 4 bytes
short   : 16 bits / 2 bytes
char    : 16 bits / 2 bytes
byte    :  8 bits / 1 bytes
boolean :  8 bits / 1 bytes

NOTE

Java reserves 8 bits for boolean datatype but uses only 1 bit

So the smallest data type in terms of memory consumption is boolean

In terms of memory allocation, boolean and byte both are smallest

NOTE

1 byte = 8 bits

Bit

The smallest unit of memory is a bit. It represents a single binary digit, either 0 or 1

Nibble

A nibble refers to four consecutive binary digits(bits) or half of a byte(i.e. 1 Nibble= 4 bits)

final

Keyword final when used with a declaration similar to a variable, creates a named constant
Syntax : final <datatype> <variable_name> = <value>;
Example:

java
final double pi = 3.14;

Types of Data Types ​

Primitive Data Types

Integer Data Types

byte , short , int , long

Floating-point Data Types

double , float

Character Data Type

char

Boolean Data Type

boolean

Reference Data Types

Arrays

Classes

Interfaces

NOTE

String is also a Reference/Non-primitive datatype (Why?)

NOTE

Primitive data types are also known as Fundamental, In-buit data types

NOTE

Reference data types are also known as Non-primitive, User-defined, Composite data types