Java Identifier

A Java identifieris any name in a Java program that are used to define a package, class, interface, method, or a variable. But technically, these identifiers must be composed of Unicode characters, numbers, currency symbols and connecting characters.

The following are the rules in declaring a Legal Java Identifier.

1.   Identifiers must start with a letter, a currency character ($), or a connecting character such as the underscore ( _ ). It can not start with a number.
2. After the first character, identifiers can contain any combination of letters, currency characters, connecting characters, or numbers.
3. There is no limit to the number of characters an identifier can contain.
4. Java reserved words are not to be used.Check this list of Java Keywords to not be used in declaring identifiers.
5. Identifiers in Java are case-sensitive.Variable SUM and sum are different when being read by the Java Compiler.

Examples of legal Identifier

 int weight;  
 int $money;  
 int _temp;  
 String _$;  
 String _temp_container;  
 String a_very_long_name_for_an_identifier;  
 String label01;  

Examples of illegal identifier;

 int .hh;   
 double money.sum;  
 int :identifier;  
 int -c;   
 int f#;  
 int 01label;  
 String volatile;