The following happens with HttpURLConnection

Consider the following code with the specs quoted

        URLConnection urlConnection = new URL("http://oracle.com").openConnection();

        // "It returns null if there are fewer than n+1 fields.
        // This method can be used in conjunction with the getHeaderFieldKey method
        // to iterate through all the headers in the message."
        System.out.println(urlConnection.getHeaderField(0));

        // Returns the key for the nth header field.
        // It returns null if there are fewer than n+1 fields.
        System.out.println(urlConnection.getHeaderFieldKey(0));

        Map<String, List<String>> headerFields = urlConnection.getHeaderFields();
        System.out.println("headerFields = " + headerFields);

The output would be:

HTTP/1.0 301 Moved Permanently
null
headerFields = {null=[HTTP/1.0 301 Moved Permanently], Connection=[close], Content-Length=[0], Location=[https://www.oracle.com/]}


getHeaderField(int) could not be used in conjunction with getHeaderFieldKey(int) and behavior of the latter doesn't conform to its specification