详解C#实例化对象的三种方式及性能对比

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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