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.