class URLConnection extends java.net.URLConnection {

    @Override
    public String getHeaderFieldKey(int index) {
		assert index >= 0 : AssertMessages.positiveOrZeroParameter();
    	switch (index) {
    	case 0:
    		return CONTENT_TYPE;
    	case 1:
    		return CONTENT_LENGTH;
    	case 2:
    		return LAST_MODIFIED;
    	default:
    	}
    	return null;
    }

    protected  URLConnection(URL url);

}