Java IO.pdf - Nguyen Dang Binh

14.3 Unicode Escapes
Java I/O
Currently, there isn't a large installed base of Unicode text editors. There's an even smaller
installed base of machines with full Unicode fonts installed. Therefore, it's essential that all
valid Java programs can be written using nothing more than ASCII characters.
All Java keywords and operators as well as the names of all the classes, methods, and fields in
the core API may be written in pure ASCII. This is by deliberate design on the part of
JavaSoft. However, Unicode characters are explicitly allowed in comments, string and char
literals, and identifiers. The following, the opening line from Homer's Odyssey, should be
legal Java:
To enable statements like that in Java source, non-ASCII characters are embedded through
Unicode escape sequences. The escape sequence for a character is a backslash ( \ ) followed
by a small u, followed by the four-digit hexadecimal code for the character. For example:
char tab = '\u0009';
char softHyphen = '\u00AD';
char sigma = '\u03C3';
char squareKeesu = '\u30B9';.
Using Unicode escapes, the opening line from Homer's Odyssey would be rendered as:
/* \u039F\u03B4\u03C5\u03C3\u03C3\u03B5\u03B9\u03B1 */
String \u03B1\u03C1\u03C7\u03B7 =
"\u0386\u03BD\u03B4\u03C1\u03B1 \u03BC\u03BF\u03B9 "
+ "\u03AD\u03BD\u03BD\u03B5\u03C0\u03B5, "
+ "\u039C\u03BF\u03C5\u03C3\u03B1, "
+ " \u03BF\u03C2 \u03BC\u03AC\u03BB\u03B1 \u03C0\u03BF\u03BB\u03BB\u03B1";
Obviously, this is horribly inconvenient for anything more than an occasional non-ASCII
character.
Many Java compilers assume that source files are written in ASCII and that the only Unicode
characters present are Unicode escapes. During a single-pass preprocessing phase, the
compiler converts each raw ASCII character or Unicode escape sequence to a two-byte
Unicode character it stores in memory. Only after preprocessing is complete and the ASCII
file has been converted to in-memory Unicode, is the file actually compiled. Some compilers
and runtimes will also compile the upper 128 characters of the ISO Latin-1 character set.
However, some do not. Worse yet, some Java virtual machines can compile files containing
non-ASCII, ISO Latin-1 characters but can't run the files they've compiled. For safety's sake
and maximum portability, you should escape all non-ASCII characters.
Version 1.1 and later of Sun's javac compiler assumes a .java file is written in the platform's
default encoding, which is Latin-1 on Solaris and Windows, MacRoman on the Mac.
However, this produces incorrect results on Windows, because Windows does not use true
Latin-1 but a modified version that includes fewer control characters and more printing
characters.
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