Java - Basic Data Type

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

Primitive Data Types:

There are eight primitive data types supported by Java. Primitive data types are predefined by the language and named by a key word. Let us now look into detail about the eight primitive data types.


byte:

  • Byte data type is a 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:

  • 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:

  • 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:

  • 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:

  • 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:

  • 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'

Java 7 Feature for numeric literal :

In Java SE 7 and later, any number of underscore characters (_) can appear anywhere between digits in a numerical literal. This feature enables you, for example, to separate groups of digits in numeric literals, which can improve the readability of your code.

For instance, if your code contains numbers with many digits, you can use an underscore character to separate digits in groups of three, similar to how you would use a punctuation mark like a comma, or a space, as a separator.

The following example shows other ways you can use the underscore in numeric literals:


long creditCardNumber = 1234_5678_9012_3456L;
long socialSecurityNumber = 999_99_9999L;
float pi = 	3.14_15F;
long hexBytes = 0xFF_EC_DE_5E;
long hexWords = 0xCAFE_BABE;
long maxLong = 0x7fff_ffff_ffff_ffffL;
byte nybbles = 0b0010_0101;
long bytes = 0b11010010_01101001_10010100_10010010;

You can place underscores only between digits; you cannot place underscores in the following places:

  • At the beginning or end of a number
  • Adjacent to a decimal point in a floating point literal
  • Prior to an F or L suffix
  • In positions where a string of digits is expected

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");