An identifier is a name given to variables, objects, and methods in Java. Identifiers must start with a letter, underscore (_), or dollar sign ($) and can include numbers but cannot be a Java keyword. Common conventions are to use lowercase names for variables and methods with uppercase names for constants. The document provides examples of valid and invalid Java identifiers.

1. Identifierswww.ustudy.in

2. IntroductionAn identifier is a collection of certain characters that could mean a variety of things

3. There are some existing Java identifiers sqrt String Integer System in outWe can make up new identifiers test1 x1 aNumber MAXIMUM A_1www.ustudy.in

4. Identifierswww.ustudy.in

5. Valid IdentifiersIdentifiers have from 1 to many characters:

6. 'a'. .'z', 'A'..'Z', '0'..'9', '_', $

7. Identifiers start with letter a1 is legal, 1a is not

8. can also start with underscore or dollar sign: _ $

9. Java is case sensitive. A and a are different.www.ustudy.in

10. Reserved IdentifierReserved identifier: Anidentifier with a pre-defined meaning that can not be changed

11. Java reserved identifiers not a complete listboolean default for new break do if private case double import public catch else instanceOf return char extends int void class float long whilewww.ustudy.in

12. IdentifiersNames given to variables, objects, methods

13. Must not be a Java keyword

14. See Appendix B for list of keywords