Java- Identifiers /Chapter - 1 /Language Fundamental

Que: What is Identifier in JAVA?
Ans:  Any name in a java program is called identifier. It can be a class name, variable name, method name, label name.

example:-
Q. How many identifiers are in the following program?

 Ans is
(D)
Description:-

Test, String & System are class names means 3.
main()  & println()are methods means 2.
args is a reference variable of String[] means 1
Hence there are total 3+2+1= 6 identifiers..Rules For Defining Java Identifier

Rules For Defining Java Identifier

Rule 1.
a to z
A to Z
0 to 9
$ and _

example:-

total_number           (valid)

total#                      (invalid) 

If we are using other than this we will get compile time error.

Rule 2.

The identifier should not begin with a digit.

example:-

123total             (invalid)

total123              (valid)

 Rule 3.

Java identifiers are case sensitive of course java language itself is created as case sensitive language. 

example:-

 int number=10;         (valid)

 int Number=20         (valid)

 int NUMBER=30;    (valid)

Above three are different values. 

Rule 4.

We can't use reserver words as identifiers.if we are trying to do then we will get compile time error. 

int x=10;        (valid)

int if=20;        (invalid)

int else=30;   (invalid) 


Rule 5.

All predefined java class name and interface name we can take as Identifiers.

example 1:-

  example 2:-

Rule 6.

There is no length for java identifiers but it is not recommended to take lengthy identifiers.

example:- 

int aaacscsvsvsscvascvncmgacvshgavg=10;  (valid)

Now you have to decide which one is a valid identifier in java.

Problem Practice:-

total_number

total#

123total

total123

Ca$h

_$_$_$_$

all@hands

JavaByChetan

Integer

Int

int

Now scroll down To check your answers:-

total_number    (valid)

total#               (invalid)

123total           (invalid)

total123          (valid)

Ca$h               (valid)

_$_$_$_$       (valid)

all@hands        (invalid)

JavaByChetan   (valid)

Integer              (valid)

Int                     (valid)

int                      (invalid)