URLStreamHandler.getHostAddress() performance

[Wang Weijun]

I am benchmarking security manager and notice this

protected synchronized InetAddress getHostAddress(URL u) {
    if (u.hostAddress != null)
        return u.hostAddress;

    String host = u.getHost();
    if (host == null || host.equals("")) {
        return null;
    } else {
        try {
            u.hostAddress = InetAddress.getByName(host);
        } catch (UnknownHostException ex) {
            return null;
        } catch (SecurityException se) {
            return null;
        }
    }
    return u.hostAddress;
}

Is there any reason why the method is synchronized? Why not simply 
"synchronized (u)"?

Thanks
Max