C# hashset,HashTable

最新推荐文章于 2025-05-27 13:37:48 发布

原创最新推荐文章于 2025-05-27 13:37:48 发布 · 311 阅读

0 ·

CC 4.0 BY-SA版权

本文对比了Java中HashMap与Hashtable的几个关键不同之处，包括同步性、对null的支持、迭代顺序预测以及性能等方面，并提供了.NET中Dictionary和HashSet的使用示例。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

.NET 没有hashmap，hashmap是Java容器；

There are several differences between HashMap and Hashtable in Java:

Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.
Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.
One of HashMap's subclasses is LinkedHashMap, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap out the HashMap for a LinkedHashMap. This wouldn't be as easy if you were using Hashtable.

Since synchronization is not an issue for you, I'd recommend HashMap. If synchronization becomes an issue, you may also look at ConcurrentHashMap

https://stackoverflow.com/questions/40471/differences-between-hashmap-and-hashtable

//dictionary
        Dictionary<byte, string> mdic = new Dictionary<byte, string>();
        mdic.Add(1, "Yaodada");
        mdic.Add(2, "Meiei");
        mdic.Add(3, "DFdsff");


        foreach(KeyValuePair<byte,string> kvp in mdic)
        {
            Console.Write("key={0},value={1}", kvp.Key, kvp.Value);
        }
        Console.WriteLine("\n");
        Console.Write("consoleWrite:"+mdic[1]+"\n");
        string name;
        if (mdic.TryGetValue(2, out name)) {
            Console.Write(name+"\n");
        }else
        {
            Console.Write("key not found..."+"\n");
        }


   //hashset
        string[] array = new string[] { "AA", "BB", "CC", "DD", "CC", "BB" };
        HashSet<string> mhash1 = new HashSet<string>(array);
        Console.Write("mhash1: "+mhash1.Count+"\n");
        foreach(string s in mhash1) {
            Console.Write(s);
        }
        Console.Write("------------------------------------"+"\n");
        string[] array2 = new string[] { "QQ", "WW", "EE", "FF", "GG" };
        HashSet<string> mhash2 = new HashSet<string>(array2);
        Console.Write("mhash2: " + mhash2.Count + "\n");
        foreach (string s in mhash2)
        {
            Console.Write(s);
        }
        Console.Write("------------------------------------" + "\n");
        mhash1.UnionWith(mhash2);
        Console.Write("new mhash1: " + mhash1.Count + "\n");
        foreach (string s in mhash1)
        {
            Console.Write(s+"\n");
        }
   //hashtable
        Hashtable mtable = new Hashtable();
        mtable.Add(1, "I");
        mtable.Add(2, "See");
        mtable.Add(3, "you");
        foreach(DictionaryEntry d in mtable)
        {
            Console.Write("key={0},value={1};\n", d.Key, d.Value);
        }
        Console.ReadKey();