Q:

Android: Should I add an empty constructor to a fragment used in ViewPager

I'm making a layout, similar to Google play's. I'm using a ViewPager which requires fragments. I'm getting a little confused now because some sites say that a fragment requires an empty constructor, but the example on developer.android.com doesn't contain a constructor. There code is just like this:
public static class DemoObjectFragment extends Fragment {
    public static final String ARG_OBJECT = "object";

    @Override
    public View onCreateView(LayoutInflater inflater,
            ViewGroup container, Bundle savedInstanceState) {
        // The last two arguments ensure LayoutParams are inflated
        // properly.
        View rootView = inflater.inflate(
                R.layout.fragment_collection_object, container, false);
        Bundle args = getArguments();
        ((TextView) rootView.findViewById(android.R.id.text1)).setText(
                Integer.toString(args.getInt(ARG_OBJECT)));
        return rootView;
    }
}

So is it required to include a constructor in a fragment or can I just leave out the constructor?

A:

The Java compiler automatically adds a default no-args constructor (which is the "empty constructor" you refer to in the question) to any class that does not feature a constructor. 
The following empty class:
public class A {
}

is equivalent to the following class with a no-args constructor with an empty body:
public class A {

    public A() {
    }

}

You are required to explicitly add a no-args constructor only when including another constructor with one or more arguments, because in this case the compiler does not add it for you.

