Java - Regex for Full Name

Question

How can I validate regex for full name? I only want alphabets (no numericals) and only spaces for the regex. This is what I have done so far. Would you please help me fix the regex? Thank you very much

public static boolean isFullname(String str) {
    boolean isValid = false;
    String expression = "^[a-zA-Z][ ]*$"; //I know this one is wrong for sure >,<
    CharSequence inputStr = str;
    Pattern pattern = Pattern.compile(expression, Pattern.CASE_INSENSITIVE);
    Matcher matcher = pattern.matcher(inputStr);
    if (matcher.matches()) {
        isValid = true;
    }
    return isValid;
}

Answer 1

This method validate the name and return false if the name has nothing or has numbers or special characters:

public static boolean isFullname(String str) {
    String expression = "^[a-zA-Z\\s]+"; 
    return str.matches(expression);        
}