How to understand the CHAR_LITERAL rule in java lexer file

[NeoZephyr]

CHAR_LITERAL:       '\'' (~['\\\r\n] | EscapeSequence) '\'';

fragment EscapeSequence
    : '\\' 'u005c'? [btnfr"'\\]
    | '\\' 'u005c'? ([0-3]? [0-7])? [0-7]
    | '\\' 'u'+ HexDigit HexDigit HexDigit HexDigit
    ;

Why '\r', '\n', ''', '\' is excluded in first part，and '\b', '\t', '\f', '"' not excluded in first part?

If I change the rule to this, is it equivalent to the previous rule

CHAR_LITERAL:       '\'' (~['\\\r\n\b\f\t\"] | EscapeSequence) '\'';

Or change it to this

CHAR_LITERAL:       '\'' (~['\\] | EscapeSequence) '\'';

[msagca]

Hi @NeoZephyr

You should refer to the Java specification to make sense of this rule.

CharacterLiteral:
' SingleCharacter '
' EscapeSequence '

SingleCharacter:
InputCharacter but not ' or \

InputCharacter:
UnicodeInputCharacter but not CR or LF

EscapeSequence:
\ b (backspace BS, Unicode \u0008)
\ s (space SP, Unicode \u0020)
\ t (horizontal tab HT, Unicode \u0009)
\ n (linefeed LF, Unicode \u000a)
\ f (form feed FF, Unicode \u000c)
\ r (carriage return CR, Unicode \u000d)
\ LineTerminator (line continuation, no Unicode representation)
\ " (double quote ", Unicode \u0022)
\ ' (single quote ', Unicode \u0027)
\ \ (backslash , Unicode \u005c)
OctalEscape (octal value, Unicode \u0000 to \u00ff)

OctalEscape:
\ OctalDigit
\ OctalDigit OctalDigit
\ ZeroToThree OctalDigit OctalDigit

OctalDigit:
(one of)
0 1 2 3 4 5 6 7

ZeroToThree:
(one of)
0 1 2 3