IDENTIFIERS:
A name in java program is called identifier. It may be class name, method name, variable name and label name.
Example:
Class Collegetak
{
publc static void main (String [] args)
{
int x=20;
}
}
In this code there are 5 identifiers
- Collegetak
- main
- String
- args
- x
Rules to define java identifiers:
Rule 1: The only allowed characters in java identifiers are:
- a to z
- A to Z
- 0 to 9
- _ (underscore)
- $
Rule 2: If we are using any other character we will get compile time error.
Example:
1) total_number-------valid
2) Total#------------------invalid
Rule 3: identifiers are not allowed to starts with digit.
Example:
- ABC123---------valid
- 123ABC---------invalid
Rule 4: java identifiers are case sensitive up course java language itself treated as case sensitive language.
Example:
class Test
{
int number=10;
int Number=20;
int NUMBER=20; we can differentiate with case.
int NuMbEr=30;
}
Rule 5: There is no length limit for java identifiers but it is not recommended to take more than 15 lengths.
Rule 6: We can't use reserved words as identifiers.
Example:
int if=10; --------------invalid
Rule 7: All predefined java class names and interface names we use as identifiers.
Example 1:
class Collegetak
{
public static void main(String[] args)
{
int String=15; System.out.println(String);
}
}
Output: 15
Example 2:
class CollegeTak
{
public static void main(String[] args)
{
int Runnable=20;
System.out.println(Runnable);
}
}
output: 20
Even though it is legal to use class names and interface names as identifiers but it is not a good programming practice.
Which of the following are valid java identifiers?
- _$_ (valid)
- Ca$h (valid)
- Java2shre (valid)
- all@hands (invalid)
- 123abc (invalid)
- Total# (invalid)
- Int ( valid)
- Integer (valid)
- int (valid)
NEXT TOPIC:RESERVED WORDS
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