public void main()
        {
            Hashtable ht = new Hashtable();
            ht.Add("key1", 12);
            ht.Add("key2", "test1");
            ht.Add("key3", 11.1);
            ht.Add("key4", "test22");
            ht.Add("key5", 12);

            //修改：
            ht["key4"] = 5.6;
            ht["key6"] = 99;  //新增一个

            //查询1
            foreach (DictionaryEntry a in ht)
            {
                object key = a.Key;
                object valur = a.Value;
                Console.WriteLine($"{key}={valur}");
            }

            //查询2
            ICollection keyList = ht.Keys;
            foreach (object k in keyList)
            {
                object key = k;
                object value = ht[k];
                Console.WriteLine($"{key}={value}");
            }
        }