BOM : Java Glossary

2007-05-04 by Roedy Green ©1996-2009 Canadian Mind Products
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BOM

Byte Order Marks are special characters at the beginning of a Unicode file to indicate whether it is big or little endian, in other words does the high or low order byte come first. These codes also tell whether the encoding is 8, 16 or 32 bit. You can recognise Unicode files by their starting byte order marks, and by the way Unicode-16 files are half zeroes and Unicode-32 files are three-quarters zeros.

UTF BOM (Byte Order Mark) Unicode-encoding Endian Indicators
0xfeff Byte-Order Mark as it appears encoded	Description
ef bb bf	UTF-8 endian, strictly speaking does not apply, though it uses big-endian most-significant-bytes first representation.
fe ff	UTF-16 for 16-bit internal UCS-2, big endian, Java network order
ff fe	UTF-16 for 16-bit internal UCS-2, little endian, Intel/Microsoft order
00 00 fe ff	UTF-32 for 32-bit internal UCS-4, big-endian, Java network order
ff fe 00 00	UTF-32 for 32-bit internal UCS-4, little endian, Intel/Microsoft order.

The actual Unicode character encoded in all cases is 0xfeff. There are also variants of these encodings that have an implied endian marker.

Unfortunately, often applications, even Javac.exe, choke on these byte order marks. Java Readers don’t automatically filter them out. There is not much you can do but manually remove them.

encoding
encoding recogniser
native2ascii.exe
Unicode
UTF

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