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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
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