I created a morse converter from a .txt file.

I'm learning java and I created a simple morse converter. Convert only A to Z and 0 to 9 chars. Space char remain for split words in morse-code. At the beginning I used a big switch for any letters or number but it was no good.

Thanks for all critiques and sorry for my bad english (I speak italian).

public static String toMorse(byte[] bytes) {
    String text = new String(bytes);
    String morseText = "";
    text = text.toLowerCase();
    String[] morseChar
            = {".-",
                "-...",
                "-.-.",
                "-..",
                ".",
                "..-.",
                "--.",
                "....",
                "..",
                ".---",
                "-.-",
                ".-..",
                "--",
                "-.",
                "---",
                ".--.",
                "--.-",
                ".-.",
                "...",
                "-",
                "..-",
                "...-",
                ".--",
                "-..-",
                "-.--",
                "--.."};
    String[] morseNumber
            = {".----",
                "..---",
                "...--",
                "....-",
                ".....",
                "-....",
                "--...",
                "---..",
                "----.",
                "-----"};

    for (int i = 0; i < text.length(); i++) {
        if (text.charAt(i) >= 'a' && text.charAt(i) <= 'z') {
            morseText = morseText + morseChar[text.charAt(i) - 'a'];
        } else if (text.charAt(i) >= '0' && text.charAt(i) <= '9') {
            morseText = morseText + morseNumber[text.charAt(i) - '0'];
        } else if (text.charAt(i) == ' ') {
            morseText = morseText + text.charAt(i);
        }
    }
    return morseText;
}