java identifiers

Question

Everywhere is said that a Java identifier can start with all characters (but not digits) including $ and _

but I noticed that methods like isJavaIdentifierStart returns true also for other chars like § , £ , € etc

Is however correct starting an identifier with there characters?

Answer 1

If isJavaIdentifierStart returns true for it, then by definition , it's a valid Java identifier starting character, because that's how the specification defines it :

Identifier:
IdentifierChars but not a Keyword or BooleanLiteral or NullLiteral
IdentifierChars:
JavaLetter
IdentifierChars JavaLetterOrDigit
JavaLetter:
any Unicode character that is a Java letter (see below)
JavaLetterOrDigit:
any Unicode character that is a Java letter-or-digit (see below)
...
A "Java letter" is a character for which the method Character.isJavaIdentifierStart(int) returns true .

Answer 2

The method means what it says.

It returns false for § , because it's not a letter, Character.getType('§') is not Character.LETTER_NUMBER , it's not a currency symbol, and it's not a connecting punctuation character.

It is true for the two currency symbols, because that is a specific criterion.