What is the difference between instantiation in constructor or in field definition?

Question

What is the difference between this:

public class Foo {
    private Bar bar;
    public Foo() { bar = new Bar(); }
}

and this:

Answer 1

To add to Darin Dimitrov's answer, initialising the fields in line is a good idea if you have several constructor overloads, and you don't want to call other overloaded constructors for some reason.