Question

我对扼杀阶级有问题。 <代码>System.String是一种类别,但为什么我们可以使用,而不必随便使用New?

例如:

Dim CommandLineParameters As String = Microsoft.VisualBasic.Interaction.Command

没有任何新的关键词

Answer 1

页: 1

Dim s As String = "hello"

你们只是指定一个参考资料。在幕后,汇编者生成密码,以瞬息万计标的<代码>hello>。这种即时情况可能发生在派任之前很久,但详细情况是另一个例子。

简言之,上述法律没有立即提出反对。

同样,在你的例子中:

Dim CommandLineParameters As String = Microsoft.VisualBasic.Interaction.Command

没有任何物体被当场。发生这种情况的是,对现有物体的提及被复制。

Answer 2

是的,汇编者有一些捷径,让你在没有明确创建的情况下使用插座。

当你使用字面直观时,甚至在你使用时,它就没有产生,相反,在申请开始时,所有字面直线都是制造的,因此,你只复制了已经存在的说明。

你的榜样类似,你没有创造新的影响力,你只是复制了已经存在的说明。

Answer 3

你可以在不立即的情况下真正使用这一工具(下文将写一些警告)。你可以:

A. 拷贝string reference to another string 参考

或

B) Add a string to a Nothing value. This has been added to simplify the using of strings. See f或 example C#: Why is adding null to a string legal? but it should be the same f或 VB.NET .

BUT

C) In VB.NET there is a big difference with C#: "internal" VB.NET functions consider Nothing to be equivalent of "". So Len(Nothing) = 0 and UCase(Nothing) = "". Methods of the string class will still throw an exception if used on Nothing (from String Manipulation and Nothing = String.Empty (Why are these equal?))

I ll add that string literals (f或 example "Foo") are pre-built during the loading of the assembly where they are defined. So if you do

Dim aString As String = "A String"

what you are doing is copying the reference of the string object containing "A String" to aString.

Answer 4

你可以。

char[] chars = {  w ,  o ,  r ,  d  };
string string1 = new string(chars);

又

string my string = "test";

that instantiates as new string with the value "test" What you are talking about is accessing Static Type members, such as String.Format or String.Join.

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