Java - Basic Data types

Basic Data types :

- 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
• Non-Primitive Type / 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 keyword. Let us now look into detail about the eight primitive data types.

byte:

• 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:

• 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'

Type	Size in Bytes	Range
byte	1 byte	-128 to 127
short	2 bytes	-32,768 to 32,767
int	4 bytes	-2,147,483,648 to 2,147,483, 647
long	8 bytes	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
float	4 bytes	approximately ±3.40282347E+38F (6-7 significant decimal digits) Java implements IEEE 754 standard
double	8 bytes	approximately ±1.79769313486231570E+308 (15 significant decimal digits)
char	2 byte	0 to 65,536 (unsigned)
boolean	not precisely defined(~ 1 byte)	true or false

Type	Default Value
byte	0
short	0
int	0
long	0
float	0.0f
double	0.0d
char	'\u0000'
boolean	false
String or other object	null

Reference Data Types:

• A Reference variable holds bits that represents a way to access an object.
• It doesn't hold the object itself, but it holds something like a pointer, or an address.
• 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");

• Reference Type Example:

Objects (Classes & Interfaces) and Arrays :

• Objects (Classes & Interfaces) and Arrays are the reference or non-primitive data types in Java.
• They are so called because they are handled by "reference" i.e. variables of their type store the address of the object or array in a variable.
• The reference type can hold three kinds of values-

class type :

Objects (Classes & Interfaces) and Arrays are the reference or non-primitive data types in Java. They are so called because they are handled by "reference" i.e. variables of their type store the address of the object or array in a variable.

The reference type can hold three kinds of values-

• Points to an object/class instance
• Whenever a variable is created, a reference to an object is also created using the name of a class for its type i.e. that variable can contain either null or a reference to an object of that class. It is not allowed to contain any other kinds of values. Such type is called reference types in Java.
• Example : 

  class Example
  {
   ...
   ...
  }
  main()
  {
   Example example1;
   Example example2;
  }
     

Interface type :

• Points to an object, which is implementing corresponding interface.
• When a class declaration implements an interface, that class inherits all of the variables and methods declared in that interface. So the implementations for all of the methods declared in the interface must be provided by that class. For example, Java provides an interface called ActionListener whose method named actionPerformed() is used to handle the different kind of event . Java also provides a class called Thread that implements Runnable interface.
• Example : 

  Runnable r;
  r = new Thread();
     

Array type :

• Points to an array instance.
• An array is a special kind of object that contains values called elements. The java array enables the user to store the values of the same type in contiguous memory allocations. The elements in an array are identified by an integer index which initially starts from 0 and ends with one less than number of elements available in the array. All elements of an array must contain the same type of value i.e. if an array is a type of integer then all the elements must be of integer type. It is a reference data type because the class named as Array implicitly extends java.lang.Object.
• Example : 

  DataType [] example1, example2, .......examplen;
  DataType [] example = new DataType [ArraySize];
  
  DataType [] example = {item 1, item 2,...item n};

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 character (xxxx)