public class MainActivity extends Activity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        FragmentManager fm = getFragmentManager();

        Fragment fragment = fm.findFragmentById(R.id.container);

        fragment = new MyFragment();

        fm.beginTransaction().add(R.id.container, fragment).commit();

    }

}

public class MyFragment extends Fragment {

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

    }

    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup parent,

            Bundle savedInstanceState) {

        View v = inflater.inflate(R.layout.fragment_main, parent, false);

        return v;

    }

}

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:id="@+id/container"

    android:layout_width="match_parent"

    android:layout_height="match_parent" />

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"

    android:layout_height="match_parent" >

    <TextView

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Hello,fragment!" />

</RelativeLayout>