便利Map集合

用KeySet()方法；

Map<Integer, String> map = new HashMap<Integer, String>();
        map.put(01, "a");
        map.put(02, "b");
        map.put(03, "c");
        map.put(04, "d");
        Set set = map.keySet();
        ArrayList<Integer> list = new  ArrayList<Integer>(set);
        for (int i = 0; i < list.size(); i++) {
            int s = list.get(i);
            System.out.println(s);
            Object o = map.get(s);
            System.out.println(o);
            System.out.println("==");