What is the difference in how these objects are instantiated?

Question

What is the difference between the two cases below:

class Data
{
    PersonDataContext persons = new PersonDataContext();
    public Data() {}
}

versus

class Data
{
    PersonDataContext persons;
    public Data() 
    {
        persons = new PersonDataContext();
    }
}

I have the same question in asp.net:

public partial class Data : System.Web.UI.Page
{
    PersonDataContext persons = new PersonDataContext();
    protected void Page_Load(object sender, EventArgs e)
    {
    }
}

versus

public partial class Data : System.Web.UI.Page
{
    PersonDataContext persons;
    protected void Page_Load(object sender, EventArgs e)
    {
        persons = new PersonDataContext();
    }
}

Answer 1

Field initializers runs before the constructor call. So In Case 1 your object of PersonDataContext will be created before the constructor call.

PersonDataContext persons = new PersonDataContext();

In 2nd case, your constructor will execute first and then it will initialize the field.

You can do a simple test

class PersonDataContext
{
    public PersonDataContext()
    {
        Console.WriteLine("In PersonDataContext Constructor");
    }
}
class Data
{
    PersonDataContext persons = new PersonDataContext();
    public Data() 
    {
        Console.WriteLine("In Data Contructor");
    }
}

class Data2
{
    PersonDataContext persons;
    public Data2() 
    {
        Console.WriteLine("In Data2 Constructor");
        persons = new PersonDataContext();
    }
}

and then in your Main method

static void Main(string[] args)
{

    Data d1 = new Data();
    Data2 d2 = new Data2();
    Console.Read();
}

Output

In PersonDataContext Constructor // Case 1

In Data Contructor //Case 1

In Data2 Constructor //Case 2

In PersonDataContext Constructor // Case 2

---

For the asp example, In first case your Field is initialized before the Page_Load event, and in 2nd case your Field is initialized in the Page_Load event