Filling and sorting the list <? expands T & S>

I am creating a set of custom swing components that implement various properties, such as requiredor tabIndex. I am having problems trying to populate Listvarious custom components and then sort the list based on tabIndexeach component.

As I try to do this, it is to implement my components using an interface Indexedthat implements a single method getIndex(). Then sort with IndexedComparator.

My classes are:

indexed:

public interface Indexed {
      public int getIndex();
}

IndexedComparator:

public class IndexedComparator implements Comparator<Indexed> {

    @Override
    public int compare(Indexed o1, Indexed o2) {
        return o1.getIndex() - o2.getIndex();
    }

}

WWTextField:

public class WWTextField extends JTextField implements Indexed, FocusListener {
    private boolean required;
    private int tabIndex;

   ...

    @Override
    public int getIndex() {
        return tabIndex;
    }
}

NewJFrame:

public class NewJFrame extends JFrame {
    List<? extends Component & Indexed> list = new ArrayList<>();
    IndexedFocusTraversalPolicy policy = new IndexedFocusTraversalPolicy();

    public NewJFrame() {
        initComponents();

        list.add(wWTextField1);
        list.add(wWTextField2);
        list.add(wWTextField3);
        list.add(wWTextField4);
        list.add(wWTextField5);
        list.add(wWFormatedTextField1);
        list.add(wWFormatedTextField2);

        Collections.sort(list);
        policy.populateComponents(list);
        this.setFocusTraversalPolicy(policy);
    }
}

Edit: I forgot to post the real question. Why is my implementation

List<? extends Component & Indexed> list = new ArrayList<>();

Job? When I try to compile, I get the following errors:

NewJFrame.java:22: error: > expected  
NewJFrame.java:22: error: ';' expected  
NewJFrame.java:22: error: illegal start of type