How/What the difference between new, Assembly.CreateInstance, and System.Activator.CreateInstance?

Question

We have several ways to create instance, how they do respectively ? i want to know the details . Is there somewhere having material to take a look? Welcome to any comments.

Sam Hobbs · Answer

Note however that forum threads are intended to also be used in the future for others to get answers.

Vulpes · Answer

Well, I'll grant you that 'static' is a term which (like many others) has different meanings in computing and can therefore be confusing to beginners. However, I don't think I have confused Steven as he said in his second post: "yes, general saying, new--statically instantiate, the others--daynamically instantiate" before going on to discuss ContextBoundObject.

Sam Hobbs · Answer

The word static can be confusing, since it also refers to classes for which multiple instances cannot be created. Also saying that "new" is used to statically instantiate an object is confusing because "new" cannot be used to instantiate a static class. I am not saying that any of that is incorrect, I am just saying that it can be confusing for people that are beginning to learn the terms. Yes, "new" is static in the sense that the object to be created is determined at compile time in the same manner that for static linking the function to be called is determined at compile time. Also for the purpose of avoiding confusion, static linking is not possible using managed code. The confusion can occur since "new" is used for classes but not static classes and static classes are not differentiated by compile time and execution time.

Vulpes · Answer

I was using the word 'statically' here in the sense that 'new' binds to the appropriate constructor at compile time, not at runtime.

Sam Hobbs · Answer

I was not familiar with the Activator Class but I looked at the documentation and I hope my explanation helps. Note that "new" is a part of the C# language but not .Net. The Activator Class is part of .Net and therefore can be used by any language that uses .Net. The "new" operator can only create objects for the one application that it is used in; it cannot be used to create objects in other computers or even not in other applications in the same computer. The Activator Class however can do all that; it looks very powerful. So you can use the Activator Class to do something in another computer, and do it as easily as if it was the same application. It might be misleading to say that "new" is used to instantiate an object statically. The word static is used for C# classes and for static linking so it's use might be confusing here. I am sure that what is meant here is that "new" is used to create a specific object whereas the Activator Class can be used to create an object that can be specified in a variable and therefore can be determined during execution (dynamically). As best as I can see, dynamic creation is not the primary purpose of the Activator Class. So is this the beginning of another creationism debate?

Vulpes · Answer

Well, with any class which inherits from MarshalByRefObject, communication across AppDomains (or across contexts) is done via a proxy. When you call 'new' in the server it will still create an instance of the class in question. However, when you call AppDomain.CreateInstance from the client, then that does create a proxy which marshals method calls back to the real object on the server.

steven · Answer

yes, general saying, new--statically instantiate, the others--daynamically instantiate. Yet, if the class is derived from ContextBoundObject, then a proxy class will be created between client class and server class, "new" object points to the proxy object.

Vulpes · Answer

'new' is used to statically instantiate an object and the other two are used to dynamically instantiate an object from its type. When you use 'new' to create an object of a certain type, the compiler is able to resolve which of the type's constructors should be called. When you use 'Activator.CreateInstance', both the type and which of its constructors to call are left to the runtime to determine using reflection. 'Assembly.CreateInstance' is just a convenience method for instantiating an object of a certain type (passed in as a string) within a particular assembly. It calls 'Activator.CreateInstance' under the hood.

How/What the difference between new, Assembly.CreateInstance, and System.Activator.CreateInstance?

Answers (8)