Java Identifiers

Language Fundamentals

Java Identifiers: A name in a java Program is called an Identifier, Which can be used for representing classes, methods, variables and labels.
Rules:
1.Java Identifier is composed of a sequence of characters, where each character may be a  ASCII Latin letters A–Z(\u0041–\u005a), and a–z (\u0061–\u007a) and for historical reasons, the ASCII underscore (_, or \u005f) and dollar sign ($, or \u0024) and ASCII digits 0-9 (\u0030–\u0039).

i.e A-Z,a-z,_,$,0-9

The $ character should be used only in mechanically generated source code or, rarely, to access pre-existing names on legacy systems.

If we use other character we will get compiled time error saying illegal character.
2. No identifier starts with the digit.
3. There is no length limit for java identifier, but SUN highly recommended up to 15 characters.
4. Identifiers in java are case sensitive.
5. We are not allowed to use reserved words (java keywords) as identifier.
6. All predefined java class names, you are allowed to use as identifiers.

Examples :

String JAVA;//Correct

String java;//Correct

String Java225; //Correct

String java1$;//Correct

String _java; //Correct

String        javal_examples;//Correct

String Runnable;//Correct and it is predefined interface name

String Seriliazable;//Correct and it is predefined interface name

String String ="Sekhar4j";//Correct and it is predefined java class String
System.out.println(String);//it prints Sekhar4j

String first-example;//Syntax error on token "first", = expected after this token

              //example cannot be resolved to a variable

String 225java2; //Syntax error on token "225", delete this token

String second1#;//   Syntax error on token "Invalid Character", delete this token