java Map的keySet和entrySet

public class MapDemo {
    public static void main(String[] args) {
        Map<String,String> map = new HashMap<String,String>();
        map.put("01","java09");
        map.put("01","java01");
        map.put("02","java02");
        map.put("03","java03");
        map.put("04","java04");

        Set<Map.Entry<String,String>> entrySet = map.entrySet();
        Iterator<Map.Entry<String,String>> it = entrySet.iterator();
        while (it.hasNext()){
            Map.Entry<String,String> m = it.next();
            System.out.println(m.getKey()+"--"+m.getValue());
        }

        Set<String> keySet = map.keySet();
        Iterator<String> i = keySet.iterator();
        while (i.hasNext()){
            String key = i.next();
            System.out.println(key+"--"+map.get(key));
        }
    }
}