Control Instances of a class

Question

I have implemented a class as below:

public class Person
{
    public int d, e, f;
    public Person()
    {
    }

    public Person(int a)
    {
    }

    public Person(int a, int b)
    {
        new Person(40, 6, 8);
    }

    public Person(int a, int b, int c)
    {
        d = a; e = b; f = c;
    }
}   

public  class Program
{
    static void Main(string[] args)
    {
        Person P = new Person(100, 200);

        Console.WriteLine("{0},{1},{2}", P.d, P.e, P.f);// it prints 0,0,0
    }
}

Now if I create the instance of Person class with two arguments I am unable to set the values of d,e,f which is because in the third constructor a new object of Person is declared all together.

So the previous object does not have any idea about this new one.

Is there any way I can get hold of this new object and assign values to d,e,f from there?

http://stackoverflow.com/questions/10377888/how-can-i-use-multiple-constructors-to-remove-duplicated-code-while-maintaining — Kaizen Programmer, May 16 '13 at 14:03

Jon Skeet · Accepted Answer · 2013-05-16T14:25:31.357

7

I think you're actually trying to chain constructors together, so that one constructor passes arguments to another:

public Person(int a, int b) : this(40, 6, 8)
{
}

It's odd that you're ignoring a and b though... normally you'd just default one value, e.g.

public Person(int a, int b) : this(a, b, 8)
{
}

See my article on constructor chaining for more details.

edited May 16 '13 at 14:25

answered May 16 '13 at 14:02

Jon Skeet

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Hi Jon, this is not an inheritance scenario. I i try to do this I get compile time error as "Person.Person cannot call itself". All I want to do is in main when I try to print the values of d,e,f I want it should be printed as 40, 6, 8. Is this possible without creating another reference of person class which has this new object, something like this:public Person x = null; public Person(int a, int b) { x = new Person(40, 6, 8); } Console.WriteLine("{0},{1},{2}", P.x.d, P.x.e, P.x.f); – ABCD May 16 '13 at 14:26
@Saurabh: Then you must have done something wrong, because the code I've posted *does* compile. I've just verified it myself. Just changing your existing two-parameter constructor overload to either of the ones I've shown is fine. I never mentioned inheritance. Unfortunately it's hard to tell exactly what you've done wrong... you should get away from the notion of having another `Person` variable in your `Person` class... I'm pretty sure you *don't* want that. You should concentrate on working out what you've done compared with the code I've shown (which really does work). – Jon Skeet May 16 '13 at 14:28
@Saurabh: I think I've found out what you've done wrong. I suspect you've added the `: this(40, 6, 8)` to the constructor which takes *3* parameters, rather than the one which takes *two* parameters. Look carefully at the code I've provided. – Jon Skeet May 16 '13 at 14:31
Sorry Jon. You are correct. this code works for me. Thanks a lot. – ABCD May 16 '13 at 14:33

score 3 · Answer 2 · answered May 16 '13 at 14:03

3

    public Person()
       : this(0,0,0)
    {
    }
    public Person(int a)
       : this(a,0,0)
    {
    }
    public Person(int a, int b)
       : this(a,b,0)
    {
    }
    public Person(int a, int b, int c)
    {
        d = a; e = b; f = c;
    }

answered May 16 '13 at 14:03

Uzzy

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14

No explanation whatsoever? – Jon Skeet May 16 '13 at 14:05
Just show what the error is. Author has to overload his contructors. – Uzzy May 16 '13 at 14:15
1

The author was already overloading the constructors. He wasn't chaining one overload to another though. I find code-only answers are *very* rarely as useful as ones which explain what's going on. – Jon Skeet May 16 '13 at 14:17

score 1 · Answer 3 · answered May 16 '13 at 14:02

1

The default value of an int is 0. Use int? and test if it has a value.

e.g.

var d = P.d.HasValue ? P.d : "";
var e = P.e.HasValue ? P.e : "";
var f = P.f.HasValue ? P.f : "";
Console.WriteLine("{0},{1},{2}", d, e, f);

answered May 16 '13 at 14:02

DaveDev

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score 1 · Answer 4 · answered May 16 '13 at 14:06

1

You can write this

    public Person(int a, int b)
        : this(40, 6, 8)
    {
    }

to call the other constructor.

answered May 16 '13 at 14:06

MBender

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How in the world did my answer get accepted and not Jon Skeet's?! THE END IS NIGH! O_O – MBender May 16 '13 at 22:22
Well, I guess balanced was restored... – MBender May 12 '15 at 08:54

Control Instances of a class

4 Answers4