Java Glossary : UTF

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UTF

UTF, or more properly UTF-8, is not intended to be human-readable. It is a compact binary-encoded form of Unicode that uses a mixture of 8, 16 and 24-bit codes. Java Strings are stored as a 16-bit big-endian length count followed by a 7-bit ASCII string. Web files don't have the length counts. Not null terminated. "ABC" == 0x0003414243. Non-ASCII-7 chars use multibyte encodings with first byte having the high bit on. UTF is an external format. UTF strings are interconverted to ordinary Strings during I/O by readUTF and writeUTF . Unicode-2 supports even 32 bit characters, and UTF has been extended to handle them as well.

Unicode	UTF	bytes required to represent the character
00000000 0xxxxxxx	0xxxxxxx	1
00000yyy yyxxxxxx	110yyyyy 10xxxxxx	2
zzzzyyyy yyxxxxxx	1110zzzz 10yyyyyy 10xxxxxx	3

UTF-8 in encoded like this:

// encode unicode-16 into UTF-8
void putwchar( char c)
   {
   if ( c < 0x80 )
      {
      putchar ( c );
      }
   else if ( c < 0x800 )
      {
      putchar ( 0xC0 | c >> 6 );
      putchar ( 0x80 | c & 0x3F );
      }
   else if ( c < 0x10000 )
      {
      putchar ( 0xE0 | c >> 12 );
      putchar ( 0x80 | c >> 6 & 0x3F );
      putchar ( 0x80 | c & 0x3F );
      }
   else if ( c < 0x200000 )
      {
      putchar ( 0xF0 | c >> 18 );
      putchar ( 0x80 | c >> 12 & 0x3F );
      putchar ( 0x80 | c >> 6 & 0x3F );
      putchar ( 0x80 | c & 0x3F );
      }
   }

UTF-7 is encoded like this, I kid you not:

view

Czyborra notes ¤ encoding ¤ Unicode

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