How to call different constructors in class using single instance of that class in C#?

Question

Here, I have created two classes Program in which Main() is present and Customer Class in which I have two Customer class constructors 1. without arguments 2. with arguments. How can i call the two constructors using single instance C1 of Customer class created in Main?

Code

using System;
public class Program
{
    public static void Main()
    {

        Customer C1 = new Customer();
        C1.PrintFullName();
        C1 = new Customer();
        C1.PrintFullName();
    }
}

class Customer
{

    string _firstName;
    string _lastName;

    public Customer() : this("No firstname","No lastname")
    {
    }

    public Customer(string FirstName, string LastName)
    {
        this._firstName = FirstName;
        this._lastName = LastName;
    }

    public void PrintFullName()
    {
        Console.WriteLine("Full Name is {0}", this._firstName+" "+this._lastName);
    }
}

Why would you want to call a constructor twice using the same instance? do you just want to reset the contents? — BugFinder
– BugFinder, Commented Jan 31, 2018 at 9:43
The parameterless constructor calls : this("No firstname","No lastname"), so you're already executing the code of both constructors. What are you trying to achieve? — C.Evenhuis
– C.Evenhuis, Commented Jan 31, 2018 at 9:53

Marc Gravell · Accepted Answer · 2018-01-31 09:45:42Z

1

A class constructor inherently is involved in creating a new object - so there is no inbuilt concept of running a constructor against an existing instance, unless you do some very nasty things that you shouldn't do.

If you want the ability to set all the properties like with a constructor, then perhaps add a method instead:

var obj = new SomeType();
obj.Init();
// ...
obj.Init("foo", "bar", 123);
// ...

Alternatively: just use the existing constructors and just accept that it'll be a different instance with a different reference:

var obj = new SomeType();
// ...
obj = new SomeType("foo", "bar", 123);
// ...

answered Jan 31, 2018 at 9:45

Marc Gravell

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4 Comments

UV009 Over a year ago

Okay. So to call different constructors in the class we only have the option of creating different instances . Can we use Singleton Pattern for this ?

Marc Gravell Over a year ago

@UV009 a singleton Customer sounds like a terrible idea, unless you're writing a client-side system that only runs in the context of a single Customer

Marc Gravell Over a year ago

@UV009 I think this is an x/y problem; you're asking about specific things like constructors and singletons, but you haven't told us what you're actually trying to achieve; so... it is very hard to comment

UV009 Over a year ago

Yes. I am learning the concepts right now. Thanks for your help.@Marc Gravell

user7867434 · Accepted Answer · 2018-01-31 09:59:05Z

0

You can find more information here:

using System;

public class Program
{
    public static void Main()
    {
        Customer C1 = new Customer("Bob", "Robert", "BobyBob 23, 41423");
        C1.PrintFullName();
        C1 = new Customer("Bob", "Robert");
        C1.PrintFullName();
    }
}

class Customer
{

    string _firstName;
    string _lastName;
    string _address;


    public Customer()
    {
        Console.WriteLine("I'm the last one :)");
        Console.WriteLine("Full Name is {0}", this._firstName+" "+this._lastName);
    }

    public Customer(string FirstName, string LastName) : this()
    {
        Console.WriteLine("I'm gonna call the constructor within the same class that has no parameters.");      
        _firstName = FirstName;
        _lastName = LastName;
    }

    public Customer(string FirstName, string LastName, string address) : this(FirstName, LastName)
    {
        Console.WriteLine("I'm gonna call the constructor within the same class that has 2 parameters that are of type string.");
        _address = _address;
    }

    public void PrintFullName()
    {
        Console.WriteLine("Full Name is {0}", this._firstName+" "+this._lastName);
    }
}

answered Jan 31, 2018 at 9:59

user7867434

5 Comments

Marc Gravell Over a year ago

it isn't at all clear to me how - if at all (which I suspect it doesn't) this answers the question at the top: "How can i call the two constructors using single instance C1 of Customer class created in Main?"

user7867434 Over a year ago

I think he wasn't sure how to put up the question since he might has not being familiar with the subject, so i assume he was referring to that.

UV009 Over a year ago

This has helped me in understanding the concept. Thank you @Gilad Reich

user7867434 Over a year ago

@UV009 Glad it helped :)

UV009 Over a year ago

I even Understood how this keyword works correctly by seeing the above code. @GiladReich

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