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

In the first case you initialize the variable at the site of declaration.

In the second, you initialize it in a constructor.

The main difference is that if you have additional constructors and either forget to initialize or chain the constructors, you can have an uninitialized variable.