Java Unicode Notes

Java Unicode Notes.txt

U+FFFF (Uniicode repesentation) is same as 0xFFFF (Hexa decimal)

To convert "U+FFFF" to code point
int codepoint=Integer.parseInt(str.substring(2), 16);

Basic Multilingual Pane (BMP) = U+00000 (    0)   to U+FFFF   (  65535) (1111111111111111 (16 1s) in Binary)
Supplementary chars           = U+10000 (65536)   to U+10FFFF (1114111)
All unicode characters        = U+00000 (    0)   to U+10FFFF (1114111)

An unicode character in Java represented by two UTF-16 characters
First character is called High Surrogate, second Low Surrogate

High Surrogate = U+D800 (55296) to U+DBFF (56319)
Low  Surrogate = U+DC00 (56320) to U+DFFF (57343)

A small set of code points are guaranteed never to be used for encoding characters,
although applications may make use of these code points internally if they wish.
There are 66 of these noncharacters: 
U+FDD0 (64976) – U+FDEF (65007)
and any code point ending in the value FFFE or FFFF (i.e., U+FFFE, U+FFFF, U+1FFFE, U+1FFFF, … U+10FFFE, U+10FFFF)

// Only BMP characters can be represented as char values in Java
int zeroWidthNonBreakingSpace = '';

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function getSurrogatePair(astralCodePoint) {
  let highSurrogate = 
     Math.floor((astralCodePoint - 0x10000) / 0x400) + 0xD800;
  let lowSurrogate = (astralCodePoint - 0x10000) % 0x400 + 0xDC00;
  return [highSurrogate, lowSurrogate];
}
getSurrogatePair(0x1F600); // => [0xDC00, 0xDFFF]

function getAstralCodePoint(highSurrogate, lowSurrogate) {
  return (highSurrogate - 0xD800) * 0x400 
      + lowSurrogate - 0xDC00 + 0x10000;
}
getAstralCodePoint(0xD83D, 0xDE00); // => 0x1F600
https://dmitripavlutin.com/what-every-javascript-developer-should-know-about-unicode/
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