前言

做项目过程中有个需求要实例化两万个对象并添加到List

中，这个过程大概需要1min才能加载完（传参较多），于是开启了代码优化之旅，再此记录。

首先想到的是可能实例化比较耗时，于是开始对每种实例化方式进行测试，过程如下

实例化方式

1、用 New 关键字实例化一个类

2、用 Activator 实例化一个类

3、用 Assembly 实例化一个类

代码实现

测试环境：

vs2019 .NET Framework 4.7

Intel Core i7-10510U CPU

首先定义一个类Person

public class Person { public Person() { } public Person(string name) { Name = name; } public string Name { get; set; }}

我们先在无参的构造函数中实例化，每种方式进行十次，每次实例化十万次，代码如下

static void Main(string[] args) { Console.WriteLine("实例化对象的耗时比较（单位：毫秒）"); Console.Write(" "); for (int i = 1; i <= 10; i++) Console.Write("{0:G}", i.ToString().PadLeft(5)); Console.Write("\n"); Console.Write("InstanceByNew".PadRight(20)); for (int i = 1; i <= 10; i++) { Person person = null; Stopwatch watch = new Stopwatch(); watch.Start(); for (int j = 0; j < 100000; j++) person = new Person(); watch.Stop(); Console.Write(watch.ElapsedMilliseconds.ToString().PadLeft(5)); } Console.Write("\n"); Console.Write("InstanceByActivator".PadRight(20)); for (int i = 1; i <= 10; i++) { Type type = Type.GetType("ConsoleApp1.Person"); Person person = null; Stopwatch watch = new Stopwatch(); watch.Start(); for (int j = 0; j < 100000; j++) { object obj = Activator.CreateInstance(type); person = obj as Person; } watch.Stop(); Console.Write(watch.ElapsedMilliseconds.ToString().PadLeft(5)); } Console.Write("\n"); Console.Write("InstanceByAssembly".PadRight(20)); for (int i = 1; i <= 10; i++) { Assembly assembly = Assembly.Load("InstancePerformance"); Person person = null; Stopwatch watch = new Stopwatch(); watch.Start(); for (int j = 0; j < 100000; j++) { object obj = assembly.CreateInstance("ConsoleApp1.Person"); person = obj as Person; } watch.Stop(); Console.Write(watch.ElapsedMilliseconds.ToString().PadLeft(5)); } Console.Write("\n"); Console.ReadKey(); }

执行结果如下：

然后来看下有参构造函数中实例化的代码和结果

static void Main(string[] args) { Console.WriteLine("实例化对象的耗时比较（单位：毫秒）"); Console.Write(" "); for (int i = 1; i <= 10; i++) Console.Write("{0:G}", i.ToString().PadLeft(5)); Console.Write("\n"); Console.Write("InstanceByNew".PadRight(20)); for (int i = 1; i <= 10; i++) { Person person = null; Stopwatch watch = new Stopwatch(); watch.Start(); for (int j = 0; j < 100000; j++) person = new Person("Test"+j); watch.Stop(); Console.Write(watch.ElapsedMilliseconds.ToString().PadLeft(5)); } Console.Write("\n"); Console.Write("InstanceByActivator".PadRight(20)); for (int i = 1; i <= 10; i++) { Type type = Type.GetType("ConsoleApp1.Person"); Person person = null; Stopwatch watch = new Stopwatch(); watch.Start(); for (int j = 0; j < 100000; j++) { object obj = Activator.CreateInstance(type,new object[]{"Test"+j}); person = obj as Person; } watch.Stop(); Console.Write(watch.ElapsedMilliseconds.ToString().PadLeft(5)); } Console.Write("\n"); Console.Write("InstanceByAssembly".PadRight(20)); for (int i = 1; i <= 10; i++) { Assembly assembly = Assembly.Load("InstancePerformance"); Person person = null; Stopwatch watch = new Stopwatch(); watch.Start(); for (int j = 0; j < 100000; j++) { object obj = assembly.CreateInstance("ConsoleApp1.Person", true, System.Reflection.BindingFlags.Default, null, new []{"Test"+j}, null, null); person = obj as Person; } watch.Stop(); Console.Write(watch.ElapsedMilliseconds.ToString().PadLeft(5)); } Console.Write("\n"); Console.ReadKey(); }

执行结果如下：

结论

从上面的执行结果可以看出这三种方式的性能排序为

New > Activator > Assembly

但使用哪种方法还要视情况而定

后续

以上可以看出New性能最高，而我就是使用的New，问题还没解决，把问题指向判断List是否存在某元素上，于是开始测试List中的Contains, Exists, Any，Where。详情请点击.

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