.NET 2.0 中 Hashtable 快速查找的方法
Loveyuki | 2007-11-24 16:13 | 991 点击 | 2 评论 | .NET 2.0，HashTable一般来说我们都是用 Hashtable 的 ContainsKey 方法来查找 Hashtable 中是否存在某个键值然后读取他，但是这个方法并不是效率最好的方法。比较好的方法是直接读取键值然后判断这个对象是否为 null 然后读取。两种代码分别如下：
- 一般慢速的方法：
if (objHash.ContainsKey(keyValue))
{
strValue=(String)objHash[keyValue];
} - 而快速的方法是：
Object objValue=objHash[keyValue];
if (objValue!=null)
{
strValue=(String)objValue;
}
两种方法的速度经过测试能差一倍左右。下面是测试代码：Hashtable objHash = new Hashtable();
for (Int32 intI = 0; intI < 1000; intI++)
{
objHash.Add("Key_" + intI.ToString(), "Value_" + intI.ToString());
}
String strValue = String.Empty;
Stopwatch timer = new Stopwatch();
timer.Start();
for (Int32 intI = 0; intI < 1000; intI++)
{
Object objValue = objHash["Key_" + intI.ToString()];
if (objValue != null)
{
strValue = (String)objValue;
}
}
timer.Stop();
Console.WriteLine("Execution time was {0:F1} microseconds.", timer.Elapsed.Ticks / 10m);
timer.Reset();
timer.Start();
for (Int32 intI = 0; intI < 1000; intI++)
{
if (objHash.ContainsKey("Key_" + intI.ToString()))
{
strValue = (String)objHash["Key_" + intI.ToString()];
}
}
timer.Stop();
Console.WriteLine("Execution time was {0:F1} microseconds.", timer.Elapsed.Ticks / 10m);
timer.Reset();
测试结果如下：
如果不需要获得对应键的值，而是只判断的话，两种方法的区别不会很明显，大家有空可以测试下。
ting
2008-04-16 13:14 #
2.0应该使用泛型的hashtable
以下代码运行时间
Execution time was 694511.1 microseconds.
Execution time was 971042.1 microseconds.
Execution time was 92339.1 microseconds.
可见有更强的速度
Dictionary<string, string> dic = new Dictionary<string, string>();
Hashtable objHash = new Hashtable();
for (Int32 intI = 0; intI < 1000000; intI++)
{
dic.Add("Key_" + intI.ToString(), "Value_" + intI.ToString());
objHash.Add("Key_" + intI.ToString(), "Value_" + intI.ToString());
}
String strValue = String.Empty;
Stopwatch timer = new Stopwatch();
timer.Start();
for (Int32 intI = 0; intI < 1000000; intI++)
{
Object objValue = objHash["Key_" + intI.ToString()];
if (objValue != null)
{
strValue = (String)objValue;
}
}
timer.Stop();
Debug.WriteLine(string.Format("Execution time was {0:F1} microseconds.", timer.Elapsed.Ticks / 10m));
timer.Reset();
timer.Start();
for (Int32 intI = 0; intI < 1000000; intI++)
{
if (objHash.ContainsKey("Key_" + intI.ToString()))
{
strValue = (String)objHash["Key_" + intI.ToString()];
}
}
timer.Stop();
Debug.WriteLine(string.Format("Execution time was {0:F1} microseconds.", timer.Elapsed.Ticks / 10m));
timer.Reset();
timer.Start();
for (Int32 intI = 0; intI < 100000; intI++)
{
if (dic.ContainsKey("Key_" + intI.ToString()))
{
strValue = dic["Key_" + intI.ToString()];
}
}
timer.Stop();
Debug.WriteLine(string.Format("Execution time was {0:F1} microseconds.", timer.Elapsed.Ticks / 10m));
timer.Reset();