자바 char 데이타 타입

The char data type (and therefore the value that a Character object encapsulates) are based on the original Unicode specification, which defined characters as fixed-width 16-bit entities. The Unicode standard has since been changed to allow for characters whose representation requires more than 16 bits. The range of legal code points is now U+0000 to U+10FFFF, known as Unicode scalar value. (Refer to the definition of the U+n notation in the Unicode standard.)
원형 유니코드 기반으로 고정된 길이 16-bit 개체로 정의된다.
유니코드 규격은 확장되어서 16비트 이상을 요구하는 표현 글자를 허락
합법적인 코드 범위는 현재 U+0000 ~ U+10FFFF


The set of characters from U+0000 to U+FFFF is sometimes referred to as the Basic Multilingual Plane (BMP). Characters whose code points are greater than U+FFFF are called supplementary characters. The Java 2 platform uses the UTF-16 representation in char arrays and in the String and StringBuffer classes. In this representation, supplementary characters are represented as a pair of char values, the first from the high-surrogates range, (\uD800-\uDBFF), the second from the low-surrogates range (\uDC00-\uDFFF).

Basic Multilingual Plane (BMP) : U+0000 to U+FFFF
Java 2 platform은 char 배열, String, StringBuffer에서 UTF-16 표현법을 사용
==> 초과되는 문자는 한 쌍의 char values 로 표현 : 

high-surrogates range (\uD800-\uDBFF)

low-surrogates range (\uDC00-\uDFFF)

 

A char value, therefore, represents Basic Multilingual Plane (BMP) code points, including the surrogate code points, or code units of the UTF-16 encoding. An int value represents all Unicode code points, including supplementary code points. The lower (least significant) 21 bits of int are used to represent Unicode code points and the upper (most significant) 11 bits must be zero. Unless otherwise specified, the behavior with respect to supplementary characters and surrogate char values is as follows:

● The methods that only accept a char value cannot support supplementary characters. They treat char values from the surrogate ranges as undefined characters. For example, Character.isLetter('\uD840') returns false, even though this specific value if followed by any low-surrogate value in a string would represent a letter.
● The methods that accept an int value support all Unicode characters, including supplementary characters. For example, Character.isLetter(0x2F81A) returns true because the code point value represents a letter (a CJK ideograph).

char 값은 BMP code points를 표현