JList repeatedly updating defaultlistmodel after selecting item 0

Question

I am using the Swing designer in Eclipse to build a GUI to list my movies which are stored in an XML file. After loading the frame and contents to the various JLists, I have the app set to update the lists when an item is selected. So, if you pick a genre, all the movies for that genre will be shown, same applies for groups, episodes and seasons. I also have a refresh lists button which reloads the lists.

the problem I am encountering is: when I have selected the item at index 0, an extra listener action is called compared to when I select index 1 or higher. Then (my main concern), if I select the refresh button, a listener is fired for every item added to the listmodel for the previously selected JList.

For example, if I select 1 from the episodes list & then refresh, only 1 listener is called. However, if I select 0 from the episode list & then refresh, I get 35 listeners called (which is the total amount of episodes in the list).

For something small like the episodes this isn't a big issue, but when this happens on the movies column I get around 1500 listeners fired.

package local.testarea;

import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.DefaultListModel;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JScrollPane;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;

import net.miginfocom.swing.MigLayout;

@SuppressWarnings( { "rawtypes", "unchecked" } )
public class ListDemo {

    private JFrame frame;
    private JList list, list_1;
    private JButton btnNewButton;
    private DefaultListModel<String> list2;
    private DefaultListModel<Integer> list1;

    /**
     * Launch the application.
     */
    public static void main( String[] args )
    {
        EventQueue.invokeLater( new Runnable() {

            public void run()
            {
                try
                {
                    ListDemo window = new ListDemo();
                    window.frame.setVisible( true );
                }
                catch ( Exception e )
                {
                    e.printStackTrace();
                }
            }
        } );
    }

    /**
     * Create the application.
     */
    public ListDemo()
    {
        list1 = new DefaultListModel<Integer>();
        list2 = new DefaultListModel<String>();
        initialize();
        updateAll();
    }

    private void updateAll()
    {
        list1.clear();
        list2.clear();
        for ( int i = 0; i < 101; i++ )
        {
            list1.addElement( i );
        }
        list2.addElement( "Even" );
        list2.addElement( "Odd" );

    }

    private void updateLists( int selected )
    {
        list1.clear();
        list2.clear();
        switch( selected )
        {
            case 0:
                for ( int i = 0; i < 101; i++)
                {
                    if ( i % 2 == 0 ) 
                    {
                        list1.addElement( i );
                    }
                }
                list2.addElement( "Even" );
                break;

            case 1:
                for ( int i = 0; i < 101; i++)
                {
                    if ( i % 2 != 0 ) 
                    {
                        list1.addElement( i );
                    }
                }
                list2.addElement( "Odd" );
                break;

            default:
                int z = selected - 10;
                list1.addElement( z );
                list2.addElement( "Even" );
                list2.addElement( "Odd" );
                break;
        }
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize()
    {
        frame = new JFrame();
        frame.setBounds( 100, 100, 450, 481 );
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        frame.getContentPane().setLayout(new MigLayout("", "[grow][grow]", "[grow][]"));

        JScrollPane scrollPane = new JScrollPane();
        frame.getContentPane().add(scrollPane, "cell 0 0,grow");

        list = new JList( list1 );
        list.addListSelectionListener(new ListSelectionListener() {
            public void valueChanged(ListSelectionEvent e) {
                System.out.println( "List 1 trigger" );
                System.out.println( "selected item: " + list_1.getSelectedIndex() );
                if ( list.getSelectedIndex() >= 0 )
                {
                    int z = 10 + list.getSelectedIndex();
                    updateLists( z );
                }
            }
        });
        scrollPane.setViewportView(list);

        JScrollPane scrollPane_1 = new JScrollPane();
        frame.getContentPane().add(scrollPane_1, "cell 1 0,grow");

        list_1 = new JList( list2 );
        list_1.addListSelectionListener(new ListSelectionListener() {
            public void valueChanged(ListSelectionEvent e) {
                System.out.println( "List 2 trigger" );
                System.out.println( "selected item: " + list_1.getSelectedIndex() );
                if ( list_1.getSelectedIndex() >= 0 )
                {
                    updateLists( list_1.getSelectedIndex() );
                }
            }
        });
        scrollPane_1.setViewportView(list_1);

        btnNewButton = new JButton("New button");
        btnNewButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                System.out.println( "refresh" );
                updateAll();
            }
        });
        frame.getContentPane().add(btnNewButton, "cell 1 1");
    }
}

Answer 1

You are modifying the lists while selection is still in progress, which causes additional selection events to be fired (recursively). You are also modifying both lists for no reason.

The String list should just act as a filter to the Integer List. Also, I don't understand why you're removing all the items from the Integer list when a single value is selected. It makes it look like a JList is not what you want to use.

In any case, I modified your ListSelectionListener:

public class ListDemo extends JFrame{

    private DefaultListModel<Integer> listModel1 = new DefaultListModel<>();
    private DefaultListModel<String> listModel2 = new DefaultListModel<>();
    private JList<Integer> list1 = new JList<>(listModel1);
    private JList<String> list2 = new JList<>(listModel2);
    int size = 101;

    public ListDemo() {

        list1.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        add(new JScrollPane(list1));

        list2.addListSelectionListener(new ListParityFilter());
        list2.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        listModel2.addElement("All");
        listModel2.addElement("Even");
        listModel2.addElement("Odd");
        list2.setSelectedIndex(0);
        add(new JScrollPane(list2), BorderLayout.EAST);

        setDefaultCloseOperation(EXIT_ON_CLOSE);
        pack();
        setLocationRelativeTo(null);
        setVisible(true);
    }

    private class ListParityFilter implements ListSelectionListener {

        public void valueChanged(ListSelectionEvent e) {

            if (e.getValueIsAdjusting())
                return;
            System.out.println("Selected List2 item: " + list2.getSelectedValue());
            listModel1.clear();
            switch (list2.getSelectedIndex()) {
                case 0:
                    for (int i = 0; i < size; i++)
                        listModel1.addElement(i);
                    break;
                case 1:
                    for (int i = 0; i < size; i += 2)
                        listModel1.addElement(i);
                    break;
                case 2:
                    for (int i = 1; i < size; i += 2)
                        listModel1.addElement(i);
                    break;
            }
        }
    }

    public static void main(String[] args) {

        new ListDemo();
    }
}

Notes:

• Instead of the refresh button, I added an "All" option for the filter list.
• The filter list should not be modified (there is no reason).
• Check for e.getValueIsAdjusting() so you don't perform unnecessary operations.
• I set the selection model to SINGLE_SELECTION for both lists.
• I removed the Integer list selection listener because it serves no purpose. It will be called once in 2 situations:
  1. When a value is selected (selected index >= 0).
  2. When a filter is applied, since the list is cleared (selected index = -1).
• Use pack() on the JFrame instead of setting its size and location.