Various data types used in java are byte, short, long, char, float, double, int, Boolean
byte :- This is in fact smallest integer type of data
types. Its width is of 8-bits with the range -128 to 127.Syntax to declare
variable as byte is as
byte i,j;
short:- This data type is also used for defining the signed
numerical variables with a width of 16-bits and having a range from -32768
to 32767. Syntax to declare variable as short is as
short a,b;
int:- This is the most commonly used data type for defining
the numerical data.
The width of this data type is 32-bit having a range
of -2,147,483,648 to 2,417,483,647. Syntax to declare variable as int is
as
int I,j;
long:- Sometimes when int is not sufficient for declaring
some data then long is used. The range of long is really very long and
it is -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807. The declaration
can be
long x,y;
float:- To represent the real number float data type can
be used. The width is 32- bit and range of this data type is 1.4e-045 to
3.4e+038. Syntax to declare variable as float is as float p,q; double:-
To represent the real number of large range the double data type is used.
Its width is 64-bit having the range 4.9e-324 to 1.8e+308. Syntax to declare
variable as byte is as
double a,b;
char:- This data type is used to represent the character
type of data. The width of this data type is 16-bit and its range is 0
to 65,536. Syntax to declare variable as byte
char a;
Boolean:- Boolean is a simple data type which denotes
a value to be either true or false.
What do you mean by Dynamic Initialization?
Java is a flexible programming language which allows the
dynamic initialization of variables. In other words, at the time of declaration
one can initialize the variables. In java we can declare the variable at
any place before it is used.
Ex.:- int a=10;
float d=2.34f;
What do you mean by Variable? What are the rules for variable declaration?
Variable is a fundamental unit of storage in java. The
variables are used in combination with identifiers, data types, operators
and some value for initialization. The syntax of variable declaration will
be:
data_type name_of_variable[=initialization];
Following are the rules for variable declaration:-
1. The variable name should not start with digits.
2. No special character is allowed in identifier except
underscore.
3. There should not be any blank space with the identifier
name.
4. The identifier name should not be a keyword.
5. The identifier name should be meaningful.
Which are of the following variable name is valid?
| Variable | Valid/Invalid | Reason |
| John | Valid | ------- |
| T_raise | Valid | ------- |
| (area) | Invalid | ( and ) not allowed |
| char | Invalid | It is keyword |
| 25th | Invalid | Digits not allowed |
| Average | Valid | ------- |
| distance | Valid | ------- |
| signed | Invalid | It is keyword |
| define | Invalid | It is keyword |
| _hello | valid | ------- |
