性能改善之For与Foreach

关于For与Foreach的区别，博客园里已经有好多这样文章了，都分析的挺好：http://www.cnblogs.com/jobs/archive/2004/07/17/25218.aspx  不过里面关于安全部分的描述可以略过。

以下是我的测试代码：

using System;
using System.Collections.Generic;
using System.Collections;
using System.Linq;
using System.Text;
using System.Diagnostics;

namespace ConApp_PerformanceTest
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] timeperiod = new string[10];
            timeperiod[0] += "testArrayListWithFor    ";
            timeperiod[1] += "testArrayListWithForEach";
            timeperiod[2] += "testArrayWithFor        ";
            timeperiod[3] += "testArrayWithForEach    ";
            timeperiod[4] += "testListWithForEach     ";
            timeperiod[5] += "testListWithFor         ";
            for (int i = 0; i < 6; i++)
            {
                Stopwatch sw = new Stopwatch();
                TestData td = new TestData();
                sw.Reset();
                sw.Start();
                td.testArrayListWithFor();
                sw.Stop();
                timeperiod[0] += "    " + sw.ElapsedMilliseconds.ToString("00000");

                sw.Reset();
                sw.Start();
                td.testArrayListWithForEach();
                sw.Stop();
                timeperiod[1] += "    " + sw.ElapsedMilliseconds.ToString("00000");

                sw.Reset();
                sw.Start();
                td.testArrayWithFor();
                sw.Stop();
                timeperiod[2] += "    " + sw.ElapsedMilliseconds.ToString("00000");

                sw.Reset();
                sw.Start();
                td.testArrayWithForEach();
                sw.Stop();
                timeperiod[3] += "    " + sw.ElapsedMilliseconds.ToString("00000");

                sw.Reset();
                sw.Start();
                td.testListWithForEach();
                sw.Stop();
                timeperiod[4] += "    " + sw.ElapsedMilliseconds.ToString("00000");

                sw.Reset();
                sw.Start();
                td.testListWithFor();
                sw.Stop();
                timeperiod[5] += "    " + sw.ElapsedMilliseconds.ToString("00000");
            }
            Console.Clear();
            for (int i = 0; i < 10; i++)
                Console.WriteLine(timeperiod[i]);
            Console.Read();

        }
    }

    class TestData
    {
        public TestData()
        {
        }
        public void testArrayListWithFor()
        {
            ArrayList sa;
            object ss;
            sa = new ArrayList();
            for (int i = 0; i < 10000000; i++)
                sa.Add("This is a string");
            for (int i = 0; i < 1000000; i++)
                ss = sa[i];
        }

        public void testArrayListWithForEach()
        {
            ArrayList sa;
            string ss;
            sa = new ArrayList();
            for (int i = 0; i < 10000000; i++)
                sa.Add("This is a string");
            foreach (string s in sa)
                ss = s;
        }

        public void testListWithForEach()
        {
            List<string> sa;
            string ss;
            sa = new List<string>();
            for (int i = 0; i < 10000000; i++)
                sa.Add("This is a string");
            foreach (string s in sa)
                ss = s;
        }

        public void testListWithFor()
        {
            List<string> sa;
            string ss;
            sa = new List<string>();
            for (int i = 0; i < 10000000; i++)
                sa.Add("This is a string");
            for (int i = 0; i < 10000000; i++)
                ss = sa[i];
        }

        public void testArrayWithFor()
        {
            string[] sa;
            string ss;
            sa = new string[10000000];
            for (int i = 0; i < 10000000; i++)
                sa[i] = "This is a string";
            for (int i = 0; i < 10000000; i++)
                ss = sa[i];
        }

        public void testArrayWithForEach()
        {
            string[] sa;
            string ss;
            sa = new string[10000000];
            for (int i = 0; i < 10000000; i++)
                sa[i] = "This is a string";
            foreach (string s in sa)
                ss = s;
        }
    }
}

　　然后是测试结果：

所以当需要改善性能的时候，不仅需要用for，而且最好是用连续的存储空间类型的集合。