Initialization in the definition versus initialization in the constructor

In Java, but also in other OO languages, is there a difference between initializing an attribute in its definition, as in

class Example {
    public Sample sample_attribute = new Sample();
}

and using the constructor to initialize it?

class Example {
    public Sample sample_attribute;

    public Example() {
        sample_attribute = new Sample();
    }
}

I could not come up with any practical difference, is there any? Otherwise, there are cases when one method is better than another, even if they have the same result?