Java - Clearing the selection in OTHER JList

Question

I have the following problem: There are 2 JLists in my frame:

    listModel = new DefaultListModel();
    ownlistModel = new DefaultListModel();
    fillList();


    ownBookList = new JList(ownlistModel);
    ownBookList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    ownBookList.setLayoutOrientation(JList.VERTICAL);
    ownBookList.setSelectedIndex(-1);



    userlist = new JList(listModel);
    userlist.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    userlist.setLayoutOrientation(JList.VERTICAL);
    userlist.setSelectedIndex(0);

Now, these are mutually exclusive, so if someone clicks an item in the one list, the previous selection in the other list should be cleared.

  ls2Handler = new ListSelectionListener(){
            @Override
                public void valueChanged(ListSelectionEvent e) {
              if (e.getValueIsAdjusting() == false) {


            //  System.out.println(ownBookList.getSelectedValue().toString().length());
                 Global.selectedUser =  ownBookList.getSelectedValue().toString();
                 Global.selectedIndex = ownBookList.getSelectedIndex();
             userlist.clearSelection();
                  updateFields(Global.selectedUser, 1);

              }


        }
    };

        lsHandler = new ListSelectionListener() {

            @Override
            public void valueChanged(ListSelectionEvent e) {
                  if (e.getValueIsAdjusting() == false) {

                //  System.out.println(userlist.getSelectedValue().toString().length());

                      Global.selectedUser =  userlist.getSelectedValue().toString();
                     Global.selectedIndex = userlist.getSelectedIndex();
                   ownBookList.clearSelection();
                      updateFields(Global.selectedUser, 0);
                  }


            }
            };


        userlist.addListSelectionListener(lsHandler);
        ownBookList.addListSelectionListener(ls2Handler);

On calling the Value is adjusting function I always get the nullpointerException:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at Books$3.valueChanged(Books.java:199) at javax.swing.JList.fireSelectionValueChanged(Unknown Source)

Why is that? As you can see, they have been declared and should be accessible.

Answer 1

Thanks to Robin I figured it out. I wasn't aware that the method clearselection() triggers the listener. It's quick and dirty but it works:

    ls2Handler = new ListSelectionListener(){
        @Override
            public void valueChanged(ListSelectionEvent e) {
          if (e.getValueIsAdjusting() == false) {

              if (ownBookList.getSelectedValue()!=null) {
                  userlist.clearSelection();
                  Global.selectedUser =  ownBookList.getSelectedValue().toString();
                  Global.selectedIndex = ownBookList.getSelectedIndex();
                  updateFields(Global.selectedUser);
              }

                else {

                    }

          }

    }
};

    lsHandler = new ListSelectionListener() {

        @Override
        public void valueChanged(ListSelectionEvent e) {
              if (e.getValueIsAdjusting() == false) {

                  if (userlist.getSelectedValue()!=null) {
                     ownBookList.clearSelection();
                      Global.selectedUser =  userlist.getSelectedValue().toString();
                      Global.selectedIndex = userlist.getSelectedIndex();
                      updateFields(Global.selectedUser);


                  }
                  else {

                  }
              }


        }
        };

Thanks again!