Installing new keyboard actions to the JList

Question

Hi I want to install replace the arrow keys and use the numpad keys to go next and previous item in JList also I dont want to show to Popup bar in gui but in the the following code it is not working for the when I install KeyboardActions to the List
import java.awt.BorderLayout;
import java.awt.event.KeyEvent;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JScrollPane;
import javax.swing.KeyStroke;
import javax.swing.ScrollPaneConstants;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;
import javax.swing.plaf.basic.BasicListUI;
import sun.swing.DefaultLookup;
public class ListOneItem extends JFrame implements ListSelectionListener {
     private static final long serialVersionUID = 1L;
     public ListOneItem() {
          final String[] numbers = {"one", "two", "three", "four", "five", "six", "seven"};
          final JList list = new JList(numbers);
          list.setVisibleRowCount(1);
          list.setSelectedIndex(0);
          list.addListSelectionListener(this);
          final JScrollPane scrollPane = new JScrollPane(list);
          scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_NEVER);
          scrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
          getContentPane().add(scrollPane, BorderLayout.NORTH);
          final MyBasicListUI listUI= new MyBasicListUI();
          list.setUI(listUI);
     class MyBasicListUI extends BasicListUI {
          @Override
          public void installKeyboardActions() {
               // get the input map
               final InputMap _im = (InputMap) DefaultLookup.get(list, this, "list.ancestorInputMap");
               // set extra keys for "selectNext" and "selectPrevious" actions
               _im.put(KeyStroke.getKeyStroke(KeyEvent.VK_NUMPAD9, 0), "selectNextRow");
               _im.put(KeyStroke.getKeyStroke(KeyEvent.VK_NUMPAD6, 0), "selectPreviousRow");
               // install the updated InputMap
               super.installKeyboardActions();
     public void valueChanged(ListSelectionEvent e) {
          final JList list = (JList) e.getSource();
          list.ensureIndexIsVisible(list.getSelectedIndex());
     public static void main(String[] args) {
          final ListOneItem frame = new ListOneItem();
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frame.setSize(200, 200);
          frame.setLocationRelativeTo(null);
          frame.setVisible(true);
}it gives the null pointer exception for the following code
final MyBasicListUI listUI= new MyBasicListUI();
list.setUI(listUI);
where I am trying to add new Keyboard Actions to the JList

Answer 1

While getting InputMap use key *"List.focusInputMap"* instaed of *"list.ancestorInputMap"* in installKeyboardActions() method.
final InputMap _im = (InputMap) DefaultLookup.get(list, this, "List.focusInputMap");Only to register new keystrokes for existing actions you don't need to have custom look and feel class. Instead modify the InputMap after list creation.
import java.awt.BorderLayout;
import java.awt.event.KeyEvent;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JScrollPane;
import javax.swing.KeyStroke;
import javax.swing.ScrollPaneConstants;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;
import javax.swing.plaf.basic.BasicListUI;
import sun.swing.DefaultLookup;
public class ListOneItemModified extends JFrame implements ListSelectionListener {
     private static final long serialVersionUID = 1L;
     public ListOneItemModified() {
          final String[] numbers = {"one", "two", "three", "four", "five", "six", "seven"};
          final JList list = new JList(numbers);
          list.getInputMap(JList.WHEN_FOCUSED).remove(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0));
          list.getInputMap(JList.WHEN_FOCUSED).remove(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0));
          list.getInputMap(JList.WHEN_FOCUSED).put(KeyStroke.getKeyStroke(KeyEvent.VK_NUMPAD9, 0), "selectNextRow");
          list.getInputMap(JList.WHEN_FOCUSED).put(KeyStroke.getKeyStroke(KeyEvent.VK_NUMPAD6, 0), "selectPreviousRow");
          list.setVisibleRowCount(1);
          list.setSelectedIndex(0);
          list.addListSelectionListener(this);
          final JScrollPane scrollPane = new JScrollPane(list);
          scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_NEVER);
          scrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
          getContentPane().add(scrollPane, BorderLayout.NORTH);
          //final MyBasicListUI listUI= new MyBasicListUI();
          //list.setUI(listUI);
//     class MyBasicListUI extends BasicListUI {
//          @Override
//          public void installKeyboardActions() {
//               // get the input map
//               final InputMap _im = (InputMap) DefaultLookup.get(list, this, "list.focusInputMap");
//               // set extra keys for "selectNext" and "selectPrevious" actions
//               _im.put(KeyStroke.getKeyStroke(KeyEvent.VK_NUMPAD9, 0), "selectNextRow");
//               _im.put(KeyStroke.getKeyStroke(KeyEvent.VK_NUMPAD6, 0), "selectPreviousRow");
//               // install the updated InputMap
//               super.installKeyboardActions();
     public void valueChanged(ListSelectionEvent e) {
          final JList list = (JList) e.getSource();
          list.ensureIndexIsVisible(list.getSelectedIndex());
     public static void main(String[] args) {
          final ListOneItemModified frame = new ListOneItemModified();
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frame.setSize(200, 200);
          frame.setLocationRelativeTo(null);
          frame.setVisible(true);
}