CODEWITHSUNDEEP
c#classoopobjectinitialization
ErsenT
ErsenT

Reputation: 29

Class instancing from a static method in C#

I have a simple question. I know that an object of a class must be initialized first to use that (non-static) class in C#.

So (I think) this piece of code does that:

namespace ConsoleApp10
{
    class Program
    {
        public class Person
        {
            public string Name;

            public void Introduce0()
            {
                Console.WriteLine("My name is " + Name + ".");
            }
        }

        static void Main(string[] args)
        {
            var person0 = new Person();
            person0.Name = "Marry";
            person0.Introduce0();
            Console.ReadKey();
        }
    }
}

And the result is:
My name is Marry.

Then I tried to the same thing with a static method:

namespace ConsoleApp10
{
    class Program
    {
        public class Person
        {
            public string Name;

            public void Introduce0()
            {
                Console.WriteLine("My name is " + Name + ".");
            }

            public static Person Introduce1(string str0)
            {
                var temp0 = new Person();
                temp0.Name = str0;
                temp0.Introduce0();
                return temp0;
            }
        }

        static void Main(string[] args)
        {
            var person0 = Person.Introduce1("Marry");
            Console.ReadKey();
        }
    }
}

And the result is, as expected, the same:
My name is Marry.

And then I added two pieces of code in my Main method:

static void Main(string[] args)
{
    var person0 = Person.Introduce1("Marry");
    person0.Name = "Sarah";
    person0.Introduce0();
    Console.ReadKey();
}

And the result is:
My name is Marry.
My name is Sarah.

So, here are my questions:
In the last example, why don't I have to initialize a Person object to access the Name field and Introduce0 method? Is accessing a static method means an auto-initialization? Or Is it because Introduce1 method has a Person object initialization in it (temp0)?

Upvotes: 2

Views: 62

Answers (2)

janw
janw

Reputation: 9616

Or Is it because Introduce1 method has a Person object initialization in it (temp0)?

Yes, exactly. Introduce1 is a static method, which means that you can call it without creating a Person object first.

Then, in Introduce1, you create a new Person object, which can subsequently be used to call instance methods of Person, like Introduce0.

Note that your code is functionally equivalent to

static void Main(string[] args)
{
    var temp0 = new Person();
    temp0.Name = "Marry";
    temp0.Introduce0();    
    var person0 = temp0;
    person0.Name = "Sarah";
    person0.Introduce0();
    Console.ReadKey();
}

Upvotes: 2

Polyfun
Polyfun

Reputation: 9639

It is the second reason: "Is it because Introduce1 method has a Person object initialization in it (temp0)?". You are initializing a Person object, which you return from Person.Introduce1. It is perfectly valid for a method in a class to return an instance of that class.

Upvotes: 0

Related Questions