java unicode 备忘

java8 字符串使用 UTF-16

public class Hex {
  public static void main(String[] args) {
    // codePoint 和 代理对的转换
    int codePoint = 0x26b99;
    System.out.println(new String(new int[]{codePoint}, 0, 1)); // 𦮙
    System.out.println("\uD85A\uDF99"); // 𦮙

    char[] chars = Character.toChars(codePoint);
    System.out.println(String.format("%#x %#x", (int) chars[0], (int) chars[1])); // 0xd85a 0xdf99

    System.out.println(new String(chars)); // 𦮙

    boolean highSurrogate = Character.isHighSurrogate(chars[0]); // true
    System.out.println(highSurrogate);
    boolean lowSurrogate = Character.isLowSurrogate(chars[1]); // true
    System.out.println(lowSurrogate);

    int toCodePoint = Character.toCodePoint(chars[0], chars[1]);
    System.out.println(Integer.toHexString(toCodePoint)); // 26b99
    int codePointAt = Character.codePointAt(chars, 0);
    System.out.println(Integer.toHexString(codePointAt)); // 26b99

    boolean supplementaryCodePoint = Character.isSupplementaryCodePoint(codePoint);
    System.out.println(supplementaryCodePoint); // true
    boolean bmpCodePoint = Character.isBmpCodePoint(codePoint);
    System.out.println(bmpCodePoint); // false
    boolean validCodePoint = Character.isValidCodePoint(codePoint);
    System.out.println(validCodePoint); // true

    int charCount = Character.charCount(codePoint);
    System.out.println(charCount); // 2

    //-----------------------------------------------------

    // 遍历字符串
    String str = "你好\uD85A\uDF99你好";
    for (int offset = 0; offset < str.length(); ) {
      int cp = str.codePointAt(offset);
      System.out.println(Integer.toHexString(cp));
      offset += Character.charCount(cp);
    }
  }
}

unicode 转 UTF-8

bytes	bits	representation
1	7	0vvvvvvv
2	11	110vvvvv 10vvvvvv
3	16	1110vvvv 10vvvvvv 10vvvvvv
4	21	11110vvv 10vvvvvv 10vvvvvv 10vvvvvv

unicode 转 UTF-16

如果U<0x10000，U的UTF-16编码就是U对应的16位无符号整数（为书写简便，下文将16位无符号整数记作WORD）。 如果U≥0x10000，我们先计算U'=U-0x10000，然后将U'写成二进制形式：yyyy yyyy yyxx xxxx xxxx，U的UTF-16编码（二进制）就是：110110yyyyyyyyyy 110111xxxxxxxxxx。

putwchar(c)
{
  if (c > 0xFFFF) { 
    putwchar (0xD7C0 + (c >> 10));
    putwchar (0xDC00 | c & 0x3FF);
  }

参考链接 www.zhihu.com/question/30… www.ibm.com/developerwo… www.jianshu.com/p/235ad9c63… www.cnblogs.com/dragon2012/… www.utf8-chartable.de/ icu-project.org/docs/papers… www.zhihu.com/question/27…