Java - generic method with bounded types for 3 similar types: String, StringBuilder, StringBuffer

Question

I know it might have no sense at all, but it's just my experiment. There are 3 types (as I know) that supports method substring(). I wan't to make a generic method like this:

public static <T extends String & StringBuilder & StringBuffer> T substr3(T str) {
        if (str.length() > 3) {
            return (T) str.substring(0, 3);
        }
        return str;
    }

It won't compile like this, because you can use as many interfaces as you need, but only one Class as bounded type. This method should work fine for this 3 types: String, StringBuilder, StringBuffer but the questions is: how to set this 3 types as bound types ?

Answer 1

Why not simply extend CharSequence?

public static <T extends CharSequence> T substr3(T str) {
    if (str.length() > 3) {
        return (T) str.subSequence(0, 3);
    }
    return str;
}

Note

CharSequence doesn't declare any substring method, but subSequence should provide the identical functionality.