1. Identifiers

2. Introduction
An identifier is a collection of certain characters that could mean a variety of things
There are some existing Java identifiers
sqrt String Integer System in out
We can make up new identifiers
test1 x1 aNumber MAXIMUM A_1

3. Identifiers

4. Valid Identifiers Identifiers have from 1 to many characters:
'a'. .'z', 'A'..'Z', '0'..'9', '_', $
Identifiers start with letter a1 is legal, 1a is not
can also start with underscore or dollar sign: _ $
Java is case sensitive. A and a are different.

5. Reserved Identifier
Reserved identifier: An identifier with a pre-defined meaning that can not be changed
Java reserved identifiers not a complete list
boolean default for new
break do if private
case double import public
catch else instanceOf return
char extends int void
class float long while

6. Identifiers Names given to variables, objects, methods
Must not be a Java keyword
See Appendix B for list of keywords
May begin with a letter or the underline character _
Followed by any number of characters, digits, or _ (note, no blanks)
Identifiers should be well chosen
use complete words (even phrases)
this helps program documentation

7. Conventions for Identifiers
Classes
Names given in lowercase except for first letter of each word in the name
Variables
Same as classes, except first letter is lowercase
Constants
All caps with _ between words
Methods
like variable names but followed by parentheses

8. Identifiers
Keywords
Lexical elements (or identifiers) that have a special, predefined meaning in the language
Cannot be redefined or used in any other way in a program
Ex: public, private, if, class, throws
See p. 32 in LL for complete list

9. Identifiers Other Identifiers Defined by programmer
Java API defines quite a few for us
e.g. System, Scanner, String, out
are used to represent names of variables, methods and classes
Cannot be keywords
We could redefine those defined in Java API if we wanted to, but this is generally not a good idea
Java IDs must begin with a letter, followed by any number of letters, digits, _ (underscore) or $ characters
Similar to identifier rules in most programming languages

10. Example for Java Identifiers
package javaidentifiers; /** * paul */ public class Main { /** args the command line arguments */ public static void main(String[] args)

11. Program
{ // TODO code application logic here System.out.println(“Must start with a letter, ($), or connecting character (_)”); System.out.println(“Can not start with a number”); System.out.println(“No limits to the amount of characters for a identifier”);

12. Program
System.out.println(“You can not use a Java Keyword”); System.out.println(“Case sensitive – IDENTIFER is different from identifier”); System.out.println(“Legal – see code”);
int _$a; int x; int $j; int _____iiii;

13. Program
System.out.println(“Illegal”); System.out.println(“int :6 – breaks rule 1″); System.out.println(“int ;J – breaks rule 1″); System.out.println(“int 6pp – breaks rule 2″); System.out.println(“int else – breaks rule 4″); }

14. The End
….. Thank You …..