List<T> 与ArrayList 性能比较

最新推荐文章于 2025-08-04 10:46:08 发布

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#ArrayList #arraylist #ListT

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本文通过实验对比了List<T>与ArrayList在值类型和引用类型下的性能表现。结果显示，在值类型的情况下，List<T>的性能明显优于ArrayList，且减少了垃圾回收的压力；而在引用类型的情况下，List<T>同样表现出更好的性能。

ValueType 情况下：这二者性能相差显著，List<T> 要好太多，且没有装箱操作，也就没有GC回收次数太多的问题。

ReferenceType：性能相差不多。不过也是前者比后者好。

    class ListTest
    {
        public static void EfficiencyTest()
        {
            ValueTypePerfTest();
            ReferenceTypePerfTest();
        }

        private static void ValueTypePerfTest()
        {
            const int count = 10000000;
            using (new OperationTimer("List<Int32>"))
            {
                List<Int32> l = new List<int>(count);
                for (Int32 n = 0; n < count; n++)
                {
                    l.Add(n);
                    Int32 x = l[n];
                }
                l = null;
            }

            using (new OperationTimer("ArrayList of Int32"))
            {
                ArrayList a = new ArrayList();
                for (Int32 n = 0; n < count; n++)
                {
                    a.Add(n);
                    Int32 x = (Int32)a[n];
                }
                a = null;
            }
        }

        private static void ReferenceTypePerfTest()
        {
            const int count = 10000000;
            using (new OperationTimer("List<String>"))
            {
                List<String> l = new List<String>(count);
                for (Int32 n = 0; n < count; n++)
                {
                    l.Add("X");
                    String x = l[n];
                }
                l = null;
            }

            using (new OperationTimer("ArrayList of String"))
            {
                ArrayList a = new ArrayList();
                for (Int32 n = 0; n < count; n++)
                {
                    a.Add("X");
                    String x = (String)a[n];
                }
                a = null;
            }
        }
    }

    internal sealed class OperationTimer : IDisposable
    {
        private Int64 m_startTime;
        private string m_Text;
        private int m_collectionCount;

        public OperationTimer(string text)
        {
            PrepareForOperation();
            m_Text = text;
            m_collectionCount = GC.CollectionCount(0);
            m_startTime = Stopwatch.GetTimestamp();
        }

        public void Dispose()
        {
            Console.WriteLine("{0, 6:###.00} Seconds (GCs = {1, 3}) {2}", (Stopwatch.GetTimestamp() - m_startTime) / (double)Stopwatch.Frequency, GC.CollectionCount(0) - m_collectionCount, m_Text);
        }

        private static void PrepareForOperation()
        {
            GC.Collect();
            GC.WaitForPendingFinalizers();
            GC.Collect();
        }
    }