Java Identifiers

What is identifier

A name in java program is called identifier. It can be a class name, method name, package name, variable name, constant name.

java-identifier-example

A shown in the above example, words marked with red underline are identifiers. As you can see there are 5 identifiers as listed below...

  1. Test (class name)
  2. main (method name)
  3. String (Library class name)
  4. args(variable name)
  5. println(method name)

Identifier naming rules

While creating identifiers, you have to remember some rules as listed below...

1. Identifier name can contains alphabets (A-Z / a-z), digits (0-9), underscore (_), dollar sign($).

contact_number (✓)
contact# (✕)

2. An identifier can't start with a digit.

abc123 (✓)
123abc (✕)

3. Spaces and special symbols are not allowed. User underscore(_) to join two or more words or use the camel-case variable name.

father name (✕)
father-name (✕)
father_name (✓)
fatherName (✓)

4. Java is a case sensitive language, so total, Total, and TOTAL are valid but different variable names.

5. Keywords and Reserved words are not allowed.

int (✕)
integer (✓)
int_number (✓)

6. Predefined class names and interface names are valid identifier names but it is not a recommended way to use predefined names.

int String = 111; (✓)
int Runnable = 555; (✓)

Valid / Invalid Identifier names

father_name  (✓)
my_number  (✓)
my# (✕)
123abc (✕)
abc123  (✓)
ca$h (✓)
_$_$_$  (✓)
contact@me (✕)
it2utor (✓)
w3schools (✓)
Integer  (✓)
int (✕)
Int  (✓)
my-address (✕)

Java Identifiers | Video Tutorial