Find out number of characters in a UTF-8 string in Java/Android

Question

I am trying to find out a string length when the string is stored in UTF-8. I tried following approach:

String str = "मेरा नाम";
Charset UTF8_CHARSET = Charset.forName("UTF-8");
byte[] abc = str.getBytes(UTF8_CHARSET);
int length = abc.length;

This gives me length of the byte array, but not number of characters in the string.

I found a website which shows both UTF-8 string length and byte length. https://mothereff.in/byte-counter Let's say my string is मेरा नाम, then I should get string length as 8 characters and not 22 bytes.

Could anyone please guide on this.

Answer 1

The shortest "length" is in Unicode code points, as notion of numbered character, UTF-32.

Correction: As @liudongmiao mentioned probably one should use:

int length = string.codePointCount(0, s.length);

In java 8:

int length = (int) string.codePoints().count();

Prior javas:

int length(String s) {
   int n = 0;
   for (int i = 0; i < s.length(); ++n) {
       int cp = s.codePointAt(i);
       i += Character.charCount(cp);
   }
   return n;
}

A Unicode code point can be encoded in UTF-16 as one or two chars.

The same Unicode character might have diacritical marks. They can be written as separate code points: basic letter + zero or more diacritical marks. To normalize the string to one (C=) compressed code point:

string = java.text.Normalizer.normalize(string, Normalizer.Form.NFC);

BTW for database purposes, the UTF-16 length seems more useful:

string.length() // Number of UTF-16 chars, every char two bytes.

(In the example mentioned UTF-32 length == UTF-16 length.)

---

A dump function

A commenter had some unexpected result:

void dump(String s) {
   int n = 0;
   for (int i = 0; i < s.length(); ++n) {
       int cp = s.codePointAt(i);
       int bytes = Character.charCount(cp);
       i += bytes;
       System.out.printf("[%d] #%dB: U+%X = %s%n",
           n, bytes, cp, Character.getName(cp));
   }
   System.out.printf("Length:%d%n", n);
}