Understanding Exceptions

Hi all,

I'm in the process of learning Java and would appreciate a bit of
guidance on the correct way to handle exceptions.

The element of code I'm working on is a simple sha2-256 hash:

private static String sha256(byte[] password, byte[] iv) {
    MessageDigest md = MessageDigest.getInstance("SHA-256");
    md.update(iv);
    byte[] hash = md.digest(password);
    return byteArrayToHexString(hash);
}

During compile this throws an unreported exception
java.security.NoSuchAlgorithmException. This in itself seems odd to me
because there is such an Algorithm as "SHA-256".

One means to handle the exception is:

private static String sha256(byte[] password, byte[] iv)
                         throws NoSuchAlgorithmException {
This appears to be a nasty solution however because every method that
calls this method is then also required to throw the same exception.

Better seems to be to catch the exception with something like:

private static String sha256(byte[] password, byte[] iv) {
    try {
        MessageDigest md = MessageDigest.getInstance("SHA-256");
        md.update(iv);
        byte[] hash = md.digest(password);
        return byteArrayToHexString(hash);
    } catch (NoSuchAlgorithmException nsae) {
    }
}

Now I've solved one problem and created another because the compiler
complains that I'm missing a return (which is true). I can insert a
false one, as in:

private static String sha256(byte[] password, byte[] iv) {
    try {
        MessageDigest md = MessageDigest.getInstance("SHA-256");
        md.update(iv);
        byte[] hash = md.digest(password);
        return byteArrayToHexString(hash);
    } catch (NoSuchAlgorithmException nsae) {
    }
    return "foobar";
}

This seems downright ugly though and is probably also evil. As the
exception never happens though, because there is such an algorithm as
"SHA-256", perhaps it is correct. Argh, brain ache! :)

Any advice would be much appreciated.

Steve