Detects if a string is made up of just emoji (and space).

EmojiDetector.java

import java.util.regex.*;

class EmojiDetector {
    private static Pattern r = Pattern.compile("^[\\s\n\r]*(?:(?:[\u00a9\u00ae\u203c\u2049\u2122\u2139\u2194-\u2199\u21a9-\u21aa\u231a-\u231b\u2328\u23cf\u23e9-\u23f3\u23f8-\u23fa\u24c2\u25aa-\u25ab\u25b6\u25c0\u25fb-\u25fe\u2600-\u2604\u260e\u2611\u2614-\u2615\u2618\u261d\u2620\u2622-\u2623\u2626\u262a\u262e-\u262f\u2638-\u263a\u2648-\u2653\u2660\u2663\u2665-\u2666\u2668\u267b\u267f\u2692-\u2694\u2696-\u2697\u2699\u269b-\u269c\u26a0-\u26a1\u26aa-\u26ab\u26b0-\u26b1\u26bd-\u26be\u26c4-\u26c5\u26c8\u26ce-\u26cf\u26d1\u26d3-\u26d4\u26e9-\u26ea\u26f0-\u26f5\u26f7-\u26fa\u26fd\u2702\u2705\u2708-\u270d\u270f\u2712\u2714\u2716\u271d\u2721\u2728\u2733-\u2734\u2744\u2747\u274c\u274e\u2753-\u2755\u2757\u2763-\u2764\u2795-\u2797\u27a1\u27b0\u27bf\u2934-\u2935\u2b05-\u2b07\u2b1b-\u2b1c\u2b50\u2b55\u3030\u303d\u3297\u3299\ud83c\udc04\ud83c\udccf\ud83c\udd70-\ud83c\udd71\ud83c\udd7e-\ud83c\udd7f\ud83c\udd8e\ud83c\udd91-\ud83c\udd9a\ud83c\ude01-\ud83c\ude02\ud83c\ude1a\ud83c\ude2f\ud83c\ude32-\ud83c\ude3a\ud83c\ude50-\ud83c\ude51\u200d\ud83c\udf00-\ud83d\uddff\ud83d\ude00-\ud83d\ude4f\ud83d\ude80-\ud83d\udeff\ud83e\udd00-\ud83e\uddff\udb40\udc20-\udb40\udc7f]|\u200d[\u2640\u2642]|[\ud83c\udde6-\ud83c\uddff]{2}|.[\u20e0\u20e3\ufe0f]+)+[\\s\n\r]*)+$");
    
    private static Boolean isEmojiOnly(String string) {
        return r.matcher(string).find();
    }
    
    private static void test(String string, Boolean isEmoji) {
        if (isEmojiOnly(string) != isEmoji) {
            System.out.println(string + " should" + (isEmoji ? "" : " not") + " be emoji only");
        }
    }
    
    public static void main(String[] args) {
        test("Hello 😲", false);
        test("-", false);
        test("+", false);
        test("$", false);
        test("👴🏻", true); // Requires Unicode 8.0 support for skin tones
        test(" 👨‍👨‍👧‍👧 ", true);
        test(" 0️⃣ ❤️", true);
        test("👨‍👨‍👧‍👧 ❤️", true);
        test(" 0️⃣ ❤️👨‍👨‍👧‍👧 ", true);
        test("0️⃣\n❤️", true);
        test("©®🔝🔛🔙💱➕➖➗®©™🔜🔴🔵⚫️⚪️🔹🔘🔸▪️▫️◻️◾️🔉🔇♦️♥️♣️♠️🀄️🎴👁‍🗨💭🗯🕔🕓🕖🕖🕜🕥💬🕎☪☪🔝☑️#️⃣#️⃣⤵️*️⃣ℹ️↩️↪️↙️↘️➡️🔂◀️🔼⏸⏯4️⃣🆓🆖📶🆒🛄🏧🌀💠✅〽️💯⁉️❕🚳🚯🚷🚫❌⭕️💢⛔️🅱㊙️✴️🆚💘💕💚🔎📝🔓🚩🎐🎀⛱🛏🗿🔑🏷🔬🏺🛡⚔🔫🛠🛠💎💴🕯📡⏲📻📞📸💾🖱📲🕍🏯🎇🏙🏜🏞🎢🚥🚦💺🚤🚇🚅🚟🚍🚜🚑🚙🎷🎺🚴🏾🎱🏉🏀🍶🍵🍿🎂🍡🍛🌭🍠🍍🍇⛄️☃🌨☀️☄⭐️🌝🌚🌚🌝🌑🌒🌕🌺🐚🕸🍃🌴🐑🐄🐄🐌🐦🐗🐽🐭💍🕶👓👠👞👨‍👩‍👧‍👦👩‍❤️‍👩🙎🏼💂🏽👥👇🏻👏🏻😿🤕😲😪🙁😟🙄😘😁🐑🌴👓👏🏻😲😘", true);
        test("㏎", false);
        test("㏷", false);
        test("䷑", false);
        test("䷫", false);
        test("䷽", false);
        test("꒞", false);
    }
}

I hard-coded ranges for some Unicode blocks. Although many code points in them are currently unassigned, it's extremely likely that they would be emoji once assigned.

\p{So}\p{Sk}\p{M} was matching a lot of things which would not be considered emoji. Now using specific code points and ranges.

Support gender.

Added support for flag tags.

How can we then find out the number of emojis if isEmojiOnly returns true?

Thanks, dude. You made great work with searching unicode blocks for emojis and making regex pattern.

Be aware that more emoji have been added to Unicode since I made this. It could use an update.