Java keywords, Java Identifiers

Java Keywords

• Keywords are simple English words which are having predefined meaning in Java Programming Language.
• Meaning of these keywords can't be modified.
• Keywords are also called Reserved Words.
• All the keywords are defined in lower case.
• We can't use keywords as names of variables, methods, classes or as any other identifiers.
• true, false, null are not keywords but reserved as Literals.
• There are 49 keywords defined up to Java 2.
• enum is new keyword add from Java 5 so there are 50 keywords from Java 5.
• const and goto are keywords but no implementation available. You can't use these keywords in Java program.

List of Keywords
Data types (8)	byte short int long float double char Boolean
Class & Object (9)	class interface enum extends implements this super new instanceof
Access Modifier (3)	private protected public
Modifier (9)	final native abstract synchronized transient volatile static const strictfp
Package (2)	package import
Control Statements (12)	if else switch case default do while break for continue return goto
Exception Handling (6)	try catch finally throw throws assert
Other type (1)	void

Identifiers

• Identifiers are the names which will be used to identify the programming elements like variable, methods, classes etc uniquely.
• Identifiers are also known as User Defined Words.

Rules to follow when we define an identifier:

• Identifier can contain Alphabets, Digits and two special symbols Dollar ($) and Underscore (_).
• First character of an identifier must be an Alphabet or Dollar ($) or Underscore (_).
• Keywords or Reserved words can't be used as Identifier.

Valid Identifier	Invalid Identifier
Hello	1stClass
Int	true
getClassName	student number
studentEmail	student-email
TOTAL_FEE	int

Other Core Java Articles:
1. Java Characteristics / features / buzzwords
2. Java basic questions
3. Java history / java editions / java versions