Binary XML file line #1: Error inflating class fragment

I'm trying to follow the Udacity Developing Android Apps course. I got to Lesson 3.03. Here, we are instructed to launch a new Activity (DetailActivity) from ForecastFragment when clicking an item in a list.

However, I keep getting an error when attempting to launch the DetailActivity. Binary XML file line #1: Error inflating class fragment, where it's caused by DetailActivity.java in it's onCreate() method.

I've already searched around, but none of the fixes suggested for this issue helped me at all.

The specific error is:

Caused by: android.app.Fragment$InstantiationException: Trying to instantiate a class
com.myapp.sunshine.app.DetailActivityFragment that is not a Fragment

DetailActivity.java

public class DetailActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_detail); //failing here
    }
}

DetailActivityFragment.java

public class DetailActivityFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_detail, container, false);
    }
 }

activity_detail.xml

<fragment xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:id="@+id/fragment"
    android:name="com.myapp.sunshine.app.DetailActivityFragment"
    tools:layout="@layout/fragment_detail" android:layout_width="match_parent"
    android:layout_height="match_parent" />

I should mention that I'm not using support libraries--as I'm targeting SDK 21+, Lollipop only.

This isn't the only fragment we've created in the course either. The other fragment we created looks identical to this one.

activity_main.xml

<fragment xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:id="@+id/fragment"
    android:name="com.myapp.sunshine.app.ForecastFragment"
    tools:layout="@layout/fragment_main" android:layout_width="match_parent"
    android:layout_height="match_parent" />

And for good measure, I'm including the ForecastFragment class. I've omitted unnecessary parts of code.

ForecastFragment.java

public class ForecastFragment extends Fragment {

    private ArrayAdapter<String> mForecaseAdapter;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setHasOptionsMenu(true);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

        String[] forecastArray = {
                "Today - Sunny - 88/63",
                "Tomorrow - Foggy - 74/58",
                "Sunday - Rainy - 65/59",
                "Monday - Cloudy - 72/67"
        };
        final List<String> weekForecast = new ArrayList<>(Arrays.asList(forecastArray));

        mForecaseAdapter = new ArrayAdapter<>(
                getActivity(),
                R.layout.list_item_forecast,
                R.id.list_item_forecast_textview,
                weekForecast);

        View rootView = inflater.inflate(R.layout.fragment_main, container, false);

        final ListView listView = (ListView) rootView.findViewById(R.id.listview_forecast);
        listView.setAdapter(mForecaseAdapter);

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
             @Override
             public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                String forecast = mForecaseAdapter.getItem(position);
                Intent detailActivityIntent = new Intent(getActivity(), DetailActivity.class)
                        .putExtra(Intent.EXTRA_TEXT, forecast);
                startActivity(detailActivityIntent);
            }
        });

        return rootView;
    }
}

fragment_detail.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".DetailActivityFragment">

<TextView android:text="@string/hello_world" android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

</RelativeLayout>

which is nearly identical to

fragment_main.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivityFragment">

<ListView
    android:id="@+id/listview_forecast"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_gravity="center" />

</FrameLayout>