Unicode knowledge

Unicode knowledge http://java.sun.com/developer/technicalArticles/Intl/Supplementary/

  String test = "镕";

  String code = Integer.toHexString(test.codePointAt(0));

  char c1 = Character.toChars(test.codePointAt(0))[0];

  int cp = Character.toCodePoint((char)0xD801, (char)0xDC00); 
A character is just an abstract minimal unit of text. It doesn't have a fixed shape (that would be a glyph), and it doesn't have a value. "A" is a character, and so is "€", the symbol for the common currency of Germany, France, and numerous other European countries.

A character set is a collection of characters. For example, the Han characters are the characters originally invented by the Chinese, which have been used to write Chinese, Japanese, Korean, and Vietnamese.

A coded character set is a character set where each character has been assigned a unique number. At the core of the Unicode standard is a coded character set that assigns the letter "A" the number 004116 and the letter "€" the number 20AC16. The Unicode standard always uses hexadecimal numbers, and writes them with the prefix "U+", so the number for "A" is written as "U+0041".

Code points are the numbers that can be used in a coded character set. A coded character set defines a range of valid code points, but doesn't necessarily assign characters to all those code points. The valid code points for Unicode are U+0000 to U+10FFFF. Unicode 4.0 assigns characters to 96,382 of these more than a million code points.

Supplementary characters are characters with code points in the range U+10000 to U+10FFFF, that is, those characters that could not be represented in the original 16-bit design of Unicode. The set of characters from U+0000 to U+FFFF is sometimes referred to as the Basic Multilingual Plane (BMP). Thus, each Unicode character is either in the BMP or a supplementary character.

A character encoding scheme is a mapping from the numbers of one or more coded character sets to sequences of one or more fixed-width code units. The most commonly used code units are bytes, but 16-bit or 32-bit integers can also be used for internal processing. UTF-32, UTF-16, and UTF-8 are character encoding schemes for the coded character set of the Unicode standard.