[ASP.NET] Dictionary 和 Hashtable 区别
Dictionary和Hashtable 是两个比较常用的表示键/值的集合,两者在实际使用过程中有何区别呢?
具体区别如下:
1. Hashtable不支持泛型,而Dictionary支持泛型。
2. Hashtable中的元素值为Object类型,所以在存储或检索值类型时通常会发生装箱和拆箱的操作,非常耗时。
3. 单线程中推荐使用Dictionary,有泛型优势。多线程中推荐使用Hashtable,默认的Hashtable允许单线程写入,多线程读取,对Hashtable进一步调用Synchronized()方法可以获得完全线程安全的类型,而Dictionary非线程安全,必须人为使用lock语句进行保护,效率大减。
4. 在通过代码测试的时候发现key是整数型Dictionary的效率比Hashtable快,如果key是字符串型,Dictionary的效率没有Hashtable快。
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/// <summary> /// key为整型,Dictionary和Hashtable效率比较 /// </summary> static void IntMethod() { Console.WriteLine("Key为整型,Dictionary和Hashtable查询性能比较:"); int count = 1000000; Dictionary<int, int> dictionary = new Dictionary<int, int>(); Hashtable hashtable = new Hashtable(); for (int i = 0; i < count; i++) { dictionary.Add(i, i); hashtable.Add(i, i); } Stopwatch stopwatch = Stopwatch.StartNew(); for (int i = 0; i < count; i++) { int value = dictionary[i]; } stopwatch.Stop(); Console.WriteLine("Dictionary:" + stopwatch.ElapsedMilliseconds); stopwatch = Stopwatch.StartNew(); for (int i = 0; i < count; i++) { object value = hashtable[i]; } stopwatch.Stop(); Console.WriteLine("Hashtable:" + stopwatch.ElapsedMilliseconds); }
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/// <summary> /// Key为字符型,Dictionary和Hashtable查询性能比较 /// </summary> static void StringMethod() { Console.WriteLine("Key为字符型,Dictionary和Hashtable查询性能比较:"); int count = 1000000; Dictionary<string, string> dictionary = new Dictionary<string, string>(); Hashtable hashtable = new Hashtable(); for (int i = 0; i < count; i++) { dictionary.Add(i.ToString(), "String"); hashtable.Add(i, i); } Stopwatch stopwatch = Stopwatch.StartNew(); for (int i = 0; i < count; i++) { string value = dictionary[i.ToString()]; } stopwatch.Stop(); Console.WriteLine("Dictionary:" + stopwatch.ElapsedMilliseconds); stopwatch = Stopwatch.StartNew(); for (int i = 0; i < count; i++) { object value = hashtable[i.ToString()]; } stopwatch.Stop(); Console.WriteLine("Hashtable:" + stopwatch.ElapsedMilliseconds); }
结果如下:
参考: