How do I recognize a character such as "ç" as a letter?

Question

I have an array of bytes that contains a sentence. I need to convert the lowercase letters on this sentence into uppercase letters. Here is the function that I did:

 public void CharUpperBuffAJava(byte[] word) {
     for (int i = 0; i < word.length; i++) {
        if (!Character.isUpperCase(word[i]) && Character.isLetter(word[i])) {
            word[i] -= 32;
        }
     }
    return cchLength;
 }

It will work fine with sentences like: "a glass of water". The problem is it must work with all ANSI characters, which includes "ç,á,é,í,ó,ú" and so on. The method Character.isLetter doesn't work with these letters and, therefore, they are not converted into uppercase.

Do you know how can I identify these ANSI characters as a letter in Java?

EDIT

If someone wants to know, I did method again after the answers and now it looks like this:

public static int CharUpperBuffAJava(byte[] lpsz, int cchLength) {
    String value;
    try {
        value = new String(lpsz, 0, cchLength, "Windows-1252");
        String upperCase = value.toUpperCase();
        byte[] bytes = upperCase.getBytes();
        for (int i = 0; i < cchLength; i++) {
            lpsz[i] = bytes[i];
        }
        return cchLength;
    } catch (UnsupportedEncodingException e) {
        return 0;
    }
}

Answer 1

You need to "decode" the byte[] into a character string. There are several APIs to do this, but you must specify the character encoding that is use for the bytes. The overloaded versions that don't use an encoding will give different results on different machines, because they use the platform default.

For example, if you determine that the bytes were encoded with Windows-1252 (sometimes referred to as ANSI).

String s = new String(bytes, "Windows-1252"); 
String upper = s.toUpperCase();