如何在日语utf-8 kanji上使用java子字符串

Question

可以使用子字符串从字符串中提取单个utf8 kanji吗？问题是utf-8“字符”的长度可以是1、2或3。

例如，"“的长度为6，因此String.substring(1，2)不能获得第一个完整字符。

在PERL中，我可以使用substr(""，1，1)获得第一个字符，或者使用substr(""，2，1)获取第二个字符。

更新:基于@msandiford的建议，我想出了这个。

public class SplitKanji {
    private String [] splitKanji;
    private SplitKanji(String string) {
        int cpCount = string.codePointCount(0, string.length());
        splitKanji = new String[cpCount];
        int nextSlot = 0;
        for (int i = 0; i < string.length();) {
            int ii = string.offsetByCodePoints(i, 1);
            splitKanji[nextSlot++] = string.substring(i, ii);
            i = ii;
        }
    }
    private String[] get() {
        return splitKanji;
    }
    public static void main(String[] args) {
        String startKanji = "私今日";
        SplitKanji myStuff = new SplitKanji(startKanji);
        String [] split = myStuff.get();
        System.out.print(startKanji + "=");
        for(String kanji: split)
            System.out.print(kanji + ":" + kanji.length() + ", ");
        System.out.println();
    }
}

Answer 1

您可以从String中提取单个Unicode代码点，如下所示：

  public static final String KANJI = "";

  public static void main(String[] args)
  {
    System.out.println(KANJI.length());                         // 6
    System.out.println(KANJI.codePointCount(0, KANJI.length()));// 3

    // Loop over each code point
    for (int i = 0; i < KANJI.length(); )
    {
      System.out.println(KANJI.codePointAt(i));
      i = KANJI.offsetByCodePoints(i, 1);
    }

    // Extract the third codepoint
    int indexForThirdCodePoint = KANJI.offsetByCodePoints(0, 2);
    int thirdCodePoint = KANJI.codePointAt(indexForThirdCodePoint);
    System.out.println(thirdCodePoint);

    // Convert codepoint back to string
    System.out.println(new String(Character.toChars(thirdCodePoint)));
  }

您可以使用上述技术获取所需代码点的开始和结束索引，然后使用substring(start, end)提取。

(编辑)所有这些都可以通过一些明智的重构和实用函数来简化。下面是一个可能的例子；我不知道您的代码的用例是什么，所以很难知道什么对您最好。

public static final String KANJI = "";

public static int lengthCodepoints(String s)
{
  return s.codePointCount(0, s.length());
}

public static String substringCodepoint(String s, int startCodepoint, int numCodepoints)
{
  int startIndex = s.offsetByCodePoints(0, startCodepoint);
  int endIndex = s.offsetByCodePoints(startIndex, numCodepoints);
  return s.substring(startIndex, endIndex);
}

public static void main(String[] args)
{
  int cpLength = lengthCodepoints(KANJI);
  for (int i = 0; i < cpLength; ++i)
  {
    System.out.println(substringCodepoint(KANJI, i, 1));
  }
}