java HashMap高效遍历

private static HashMap<String, String> userDomain = new HashMap<String, String>();

Iterator<Entry<String, String>> iter = userDomain.entrySet().iterator();
        while(iter.hasNext()) {
            Entry<String, String> entry = iter.next();
            String key = entry.getKey();
            String val = entry.getValue();
            System.out.println(key + ":" + val);
        }