November 24, 2013

Published November 24, 2013 by

Java Data Types

Data Types: A data type or simply type is a classification identifying one of various types of data, such as whole numbers or fractional numbers.

Data Type determines:
  • the possible values for that type
  • the operations that can be done on values of that type
  • the meaning of the data
  • the way values of that type can be stored
Java is a strongly typed language because when you declare a variable, you must specify the variable’s type. Then the compiler ensures that the wrong type data is not assigned to the variable.

Java data types are mainly of two types:
  • Primitive Types
  • Reference Types
Primitive Types:
  • Primitive types are defined by the language itself. 
  • The memory location of primitive type variable contains the actual value of the variable
Reference Types:
  • Reference types are defined by classes in Java API or by classes created by the developers rather than by the language itself.
  • The memory location of reference type variable contains an address that indicates the memory location of the actual object.

Primitive Types vs. Reference Type:
Primitive Types
Reference Types
1. Primitive types are the fundamental, built in (as keyword) types
1. Reference types are constructed from primitive types either through class definition, interface definition or the use of arrays.
2. A variable of any primitive type contains a single value of the appropriate size and format.
2. A variable of a reference type holds a null reference or a reference to an instance of a class
3. Values of these types cannot be decomposed
3. A reference type can be decomposed into several values.

List of Primitive Types:
Types
Characteristics
Memory Size (byte)
Minimum Value
Maximum Value
byte
Whole numbers
1
 -128
127 
short
2
-32768
32767
int
4
-2147483648
2147483647
long
8
-9223372036854775808
9223372036854775807
float
Fractional numbers
4
1.4E-45
3.4028235E38
double
8
4.9E-324
1.7976931348623157E308
char
Any single symbol
2
'\u0000', that is 0
'\uffff' that is 65535
boolean
true/false
1



Reference Types Example:
Java classes, interfaces and arrays are reference types.
  • String
  • Date
  • And many more …
Further reading:

,