Displaying UTF-8 Emoji in Java

Question

Say I have the 😈 (devil) emoji.

In 4-byte UTF-8, it's represented like so: \u00f0\u009f\u0098\u0088

However, in Java, it will only print correctly like so: \ud83d\ude08

How would I convert from the first to the second?

UPDATE 2

MNEMO's answer is much simpler, and answers my question, so it's probably better to go with his solution.

UPDATE

Thanks Basil Bourque for the write-up. It was very interesting.

I found a good reference here: https://github.com/pRizz/Unicode-Converter/blob/master/conversionfunctions.js (particularly the convertUTF82Char() function).

For anyone wandering by here in the future, here's what that looks like in Java:

public static String fromCharCode(int n) {
    char c = (char)n;
    return Character.toString(c);
}

public static String decToChar(int n) {
    // converts a single string representing a decimal number to a character
    // note that no checking is performed to ensure that this is just a hex number, eg. no spaces etc
    // dec: string, the dec codepoint to be converted
    String result = "";
    if (n <= 0xFFFF) {
        result += fromCharCode(n);
    } else if (n <= 0x10FFFF) {
        n -= 0x10000;
        result += fromCharCode(0xD800 | (n >> 10)) + fromCharCode(0xDC00 | (n & 0x3FF));
    } else {
        result += "dec2char error: Code point out of range: " + decToHex(n);
    }

    return result;
}

public static String decToHex(int n) {
    return Integer.toHexString(n).toUpperCase();
}

public static String convertUTF8_toChar(String str) {
    // converts to characters a sequence of space-separated hex numbers representing bytes in utf8
    // str: string, the sequence to be converted
    var outputString = "";
    var counter = 0;
    var n = 0;

    // remove leading and trailing spaces
    str = str.replaceAll("/^\\s+/", "");
    str = str.replaceAll("/\\s+$/", "");
    if (str.length() == 0) {
        return "";
    }

    str = str.replaceAll("/\\s+/g", " ");

    var listArray = str.split(" ");
    for (var i = 0; i < listArray.length; i++) {
        int b = parseInt(listArray[i], 16); // alert('b:'+dec2hex(b));
        switch (counter) {
            case 0:
                if (0 <= b && b <= 0x7F) { // 0xxxxxxx
                    outputString += decToChar(b);
                } else if (0xC0 <= b && b <= 0xDF) { // 110xxxxx
                    counter = 1;
                    n = b & 0x1F;
                } else if (0xE0 <= b && b <= 0xEF) { // 1110xxxx
                    counter = 2;
                    n = b & 0xF;
                } else if (0xF0 <= b && b <= 0xF7) { // 11110xxx
                    counter = 3;
                    n = b & 0x7;
                } else {
                    outputString += "convertUTF82Char: error1 " + decToHex(b) + "! ";
                }
                break;
            case 1:
                if (b < 0x80 || b > 0xBF) {
                    outputString += "convertUTF82Char: error2 " + decToHex(b) + "! ";
                }
                counter--;
                outputString += decToChar((n << 6) | (b - 0x80));
                n = 0;
                break;
            case 2:
            case 3:
                if (b < 0x80 || b > 0xBF) {
                    outputString += "convertUTF82Char: error3 " + decToHex(b) + "! ";
                }
                n = (n << 6) | (b - 0x80);
                counter--;
                break;
        }
    }

    return outputString.replaceAll("/ $/", "");
}

Pretty much a 1-for-1 copy, but it accomplishes my goal.

Answer 1

well, this is quite unnecessary to add, but after you understand all character encoding system and Unicode concept, following code might work for you.

byte[] a = { (byte)0xf0, (byte)0x9f, (byte)0x98, (byte)0x88 };
String s = new String(a,"UTF-8");
byte[] b = s.getBytes("UTF-16BE");
for ( byte c : b ) { System.out.printf("%02x ",c); }