LEXICAL STRUCTURE

Line Terminators

3.4

RawInputCharacter:

any Unicode character

HexDigit: one of

0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F

The

\

,

u

, and hexadecimal digits here are all ASCII characters.

In addition to the processing implied by the grammar, for each raw input char 

acter that is a backslash

\

, input processing must consider how many other

\

 char 

acters contiguously precede it, separating it from a non 

\

 character or the start of

the input stream. If this number is even, then the

\

 is eligible to begin a Unicode

escape; if the number is odd, then the

\

 is not eligible to begin a Unicode escape.

For example, the raw input

"\\u2297=\u2297"

 results in the eleven characters

" \ \ u 2 2 9 7 =

"

 (

\u2297

 is the Unicode encoding of the character  

)

.

If an eligible

\

 is not followed by

u

, then it is treated as a

RawInputCharacter

and remains part of the escaped Unicode stream. If an eligible

\

 is followed by

u

,

or more than one

u

, and the last

u

 is not followed by four hexadecimal digits, then

a compile time error occurs.

The character produced by a Unicode escape does not participate in further

Unicode escapes. For example, the raw input

\u005cu005a

 results in the six char 

acters

\ u 0 0 5 a

, because

005c

 is the Unicode value for

\

. It does not result in

the character

Z

, which is Unicode character

005a

, because the

\

 that resulted from

the

\u005c

 is not interpreted as the start of a further Unicode escape.

Java specifies a standard way of transforming a Unicode Java program into

ASCII that changes a Java program into a form that can be processed by ASCII 

based tools. The transformation involves converting any Unicode escapes in the

source text of the program to ASCII by adding an extra

u

 for example,

\uxxxx

becomes

\uuxxxx

 while simultaneously converting non ASCII characters in the

source text to a

\uxxxx

 escape containing a single

u

. This transformed version is

equally acceptable to a Java compiler and represents the exact same program. The

exact Unicode source can later be restored from this ASCII form by converting

each escape sequence where multiple

u

's are present to a sequence of Unicode

characters with one fewer

u

, while simultaneously converting each escape

sequence with a single

u

 to the corresponding single Unicode character.

Java systems should use the

\uxxxx

 notation as an output format to display

Unicode characters when a suitable font is not available.

3.4   Line Terminators

Java implementations next divide the sequence of Unicode input characters into

lines by recognizing

line terminators

. This definition of lines determines the line

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