Leet.java

import java.util.HashMap;
import java.util.Map;
import java.util.Random;

/**
 * @author superblaubeere27, Bon (https://stackoverflow.com/questions/33416987/java-simple-english-to-leet-converter)
 */
public class Leet {
    static char leet[] = {'4', '8', '(', ')', '3', '}', '6', '#', '!', ']', 'X', '1', 'M', 'N', '0', '9', 'Q', '2', 'Z', '7', 'M', 'V', 'W', 'X', 'J', 'Z'};

    static HashMap<String, String> replace = new HashMap<String, String>();

    static {
        replace.put("HACKER", "HAX0R");
    }

    private static String toLeet(String s) {
        StringBuilder result = new StringBuilder();

        Random rand = new Random();

        String str = s.toUpperCase(); // convert all to upper case so that you don't need equalsIgnoreCase()

        for (Map.Entry<String, String> stringStringEntry : replace.entrySet()) {
            str = str.replace(stringStringEntry.getKey(), stringStringEntry.getValue());
        }

        for (int i = 0; i < str.length(); ++i) {
            char c = str.charAt(i);
            if ((c - 'A') < 0 || (c - 'A') > leet.length) {
                result.append(c);
                continue;
            }
            result.append(rand.nextBoolean() ? leet[c - 'A'] : Character.toLowerCase(leet[c - 'A'])); // Str.charAt(i) - 'A' this will give you the correct index in leet
        }
        return result.toString();
    }
}

xD