What's the difference between a default constructor and just initializing an object's fields directly?

What reasons are there to prefer one of the following examples over the other?

Example 1

public class Foo
{
    private int x = 5;
    private String[] y = new String[10];
}

Example 2

public class Foo
{
    private int x;
    private String[] y;

    public Foo()
    {
        x = 5;
        y = new String[10];
    }
}