public class Test{
    public static void main(String[] args) {
        try (BufferedReader reader = new BufferedReader(new FileReader("test.txt"))) {
            long[] unicodeArray = new long[65536];

            while (reader.ready()) {
                char[] charArray = reader.readLine().toCharArray();
                for (char c : charArray) {
                    unicodeArray[(int) c]++;
                }
            }

            for (int i = 0; i < unicodeArray.length; i++) {
                if (unicodeArray[i] > 0) {
                    System.out.println("Symbol: " + (char) i + " Freq: " + unicodeArray[i]);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

try (InputStream reader = new FileInputStream("test.txt")) {
    long[] unicodeArray = new long[65536];
    byte[] buf = new byte[4096];
    int len;
    short maxChar;
    long maxCharCnt = 0;

    while ((len = reader.read(buf)) > 0) {
        for (int i = 0; i < len; i += 2) {
            short c = (buf[i] << 8) || (buf[i + 1] & 0xff);
            unicodeArray[c]++;
            if (unicodeArray[c] > maxCharCnt) {
                maxChar = c;
                maxCharCnt = unicodeArray[c];
        }
    }

    System.out.println((char)maxChar);
}