Java Identifiers identifiers and language keywords

Identifiers are used to name elements of Java programs, such as classes, interfaces, variables, methods, constructors, and arguments. A valid name begins with a Unicode letter, underscore character (_), or dollar sign ($). A Unicode letter is an English letter (a-z) or (A-Z) or a letter in a non-English language. The second and remaining letters of an identifier may be a Unicode letter, underscore, dollar sign, or digit (0-9). The dollar sign character is used by compiler-internal identifiers and should be avoided. Identifiers are case sensitive. The identifiers myID and MyID are considered to be separate identifiers. An identifier may not use the literal values, true, false, null, or any of the keywords that are reserved by Java. Keywords may not be used as Java variables.

The Java Language Specification draws a distinction between keywords and literal values. It states that while true and false might appear to be keywords, they are technically Boolean literals. Similarly, while null might appear to be a keyword, it is technically the null literal. Why does the language specification do this? If it considered the literals true, false, and null as keywords, then it would also have to include the other literal values as keywords. By excluding true, false, null, and the other literal values, it is able to keep the keyword list to a manageable size.
Keywords are words that are used as part of a code structure, like for or while. They change the way a compiler handles a block of code, e.g. a for tells the compiler to execute the code within the specified scope repeatedly,until the given exit condition is reached. The class keyword tells the compiler to treat everything within the specified scope to be part of a particular class. Keyword names are reserved, so you can not use them as variable names. Literals like true, false and null are values that can be assigned, but their names are reserved in the same way that keywords are, i.e. you cannot have a variable called true or for. They make up parts of expressions.

• Literal Values for All Primitive Types
  A primitive literal is merely a source code representation of the primitive data types, in other words, an integer, floating-point number, boolean, or character that you type in while writing code. The following are examples of primitive literals:
  

  'b'          // char literal
  42         // int literal
  false     // boolean literal
  89.343 // double literal		
  

The Java language reserves a list of 53 keywords.

abstract	assert	boolean	break
byte	case	catch	char
class	const	continue	default
do	double	else	enum
extends	false	final	finally
float	for	goto	if
implements	import	instanceof	int
interface	long	native	new
null	package	private	protected
public	return	short	static
strictfp	super	switch	synchronized
this	throw	throws	transient
true	try	void	volatile
while

In Java SE 22, the total number of keywords remains 53, which is the same number as in Java SE 7. Although new features and functionalities have been introduced in Java since version 7, no new keywords have been added to the language after Java SE 7. However, Java has evolved by adding new constructs and enhancements such as records, pattern matching, and sealed classes, but these have been implemented without the need for introducing additional keywords.

Click the Quiz link below to check your understanding of the main() method, identifiers, and keywords.
Keyword Identifier - Quiz