Data type is a spacial keyword used to allocate sufficient memory space for the data, in other words, Data type is used for representing the data in the main memory (RAM) of the computer.
In general every programming language is containing three categories of data types. They are
· Fundamental or primitive data types
· Derived data typesUser defined data types.
Primitive data types
Contents
Primitive data types are those whose variables allows us to store only one value but they never allows us to store multiple values of same type. This is a data type whose variable can hold maximum one value at a time.
Example
int a; // valid
a=10; // valid
a=10,20,30; // invalid Here “a” store only one value at a time because it is primitive type variable.
Derived data types
Derived data types are those whose variables allow us to store multiple values of same type. But they never allows to store multiple values of different types. These are the data type whose variable can hold more than one value of similar type. In general derived data type can be achieve using array.
Example
int a[]={10,20,30}; // valid int b[]={100,'A',"ABC"}; // invalid Here derived data type store only same type of data at a time not store integer, character and string at same time.
User defined data types
User defined data types are those which are developed by programmers by making use of appropriate features of the language.
User defined data types related variables allows us to store multiple values either of same type or different type or both. This is a data type whose variable can hold more than one value of dissimilar type, in java it is achieved using class concept.
Note: In java both derived and user defined data type combined name as reference data type.
In C language, user defined data types can be developed by using struct, union, enum etc. In java programming user defined datatype can be developed by using the features of classes and interfaces.
In java we have eight data type which are organized in four groups. They are
- Integer category data types
- Character category data types
- Float category data types
- Boolean category data types
Integer category data types
These category data types are used for storing integer data in the main memory of computer by allocating sufficient amount of memory space.Integer category data types are divided into four types which are given in following table
| Data Type | Size | Range | |
| 1 | byte | 1 | + 127 to -128 |
| 2 | short | 2 | + 32767 to -32768 |
| 3 | int | 4 | + x to – (x+1) |
| 4 | long | 8 | + y to – (y+1) |
Character category data types
A character is an identifier which is enclosed within single quotes. In java to represent character data, we use a data type called char. This data type takes two byte since it follows Unicode character set.
| Data Type | Size(Byte) | Range |
| char | 2 | 32767 to -32768 |
Why Java take 2 byte of memory for store character ?
Because java uses Unicode system rather than ASCII code system. \u0000 is the lowest range of Unicode system.
Unicode System
Unicode is a universal international standard character encoding that is capable of representing most of the world’s written languages.
Before Unicode, there were many language standards:
ASCII (American Standard Code for Information Interchange) for the United States.
ISO 8859-1 for Western European Language.
KOI-8 for Russian.
GB18030 and BIG-5 for Chinese, and so on.
This caused two problems:
1. A particular code value corresponds to different letters in the various language standards.
2. The encodings for languages with large character sets have variable length. Some common characters are encoded as single bytes, other require two or more byte.
To solve these problems,:-
A new language standard was developed i.e. Unicode System. In Unicode, character holds 2 byte, so java also uses 2 byte for characters.
lowest value:\u0000
highest value:\uFFFF
Java support more than 18 international languages so java take 2 byte for characters, because for 18 international language 1 byte of memory is not sufficient for storing all characters and symbols present in 18 languages. Java supports Unicode but c support ascii code. In ascii code only English language are present, so for storing all English latter and symbols 1 byte is sufficient. Unicode character set is one which contains all the characters which are available in 18 international languages and it contains 65536 characters
Float category data types
Float category data type are used for representing float values. This category contains two data types, they are in the given table
| Data Type | Size | Range | Number of decimal places |
| float | 4 | +2147483647 to -2147483648 | 8 |
| double | 8 | + 9.223*1018 | 16 |
Boolean category data types
Boolean category data type is used for representing or storing logical values is true or false. In java programming to represent Boolean values or logical values, we use a data type called Boolean.
QUE-Why Boolean data types take zero byte of memory?
ANS-Boolean data type takes zero bytes of main memory space because Boolean data type of java implemented by Sun Micro System with a concept of flip – flop. A flip – flop is a general purpose register which stores one bit of information (one true and zero false).
