我想将动作侦听器从一个JList添加到另一个JList，并且JList如何在没有任何文本的情况下出现？

Question

I need help with htis issue I have with Javan swing. I have three JLists in my GUI. One of the list contains a menu for a restaurant. The cashier is supposed to click on the a dish on the first JList and whatever he clicked should appear on the second JList. How can i do this?

Also another problem is that I cant hae the JList appear UNLESS i am giving it an array object to display the menu, I want the JList to appear while its empty as well, how can i do that?

    import java.awt.*; 
    import java.awt.event.*;


    import javax.swing.*;


    public class frame extends JFrame {
    private JList menuList ; 
    private JList orderList; 
    private JLabel countLabel; 
    private DefaultListModel listModel; 
    private Dimension menuListDimension; 



    public frame (){
    JFrame frame = new JFrame ();
    frame.setDefaultCloseOperation(DISPOSE_ON_CLOSE);
    buildUI(); 
    }
    private void buildUI () {
        BoxLayout mainLayout = new BoxLayout(getContentPane(), BoxLayout.X_AXIS);
        getContentPane().setLayout(mainLayout);

    getContentPane().add(Box.createHorizontalGlue());
    getContentPane().add(buildMenuPanel()); 
    getContentPane().add(Box.createHorizontalStrut(0));
    getContentPane().add(buildOrderPanel());  
    getContentPane().add(Box.createHorizontalStrut(10));
    getContentPane().add(buildPayPanel());
    getContentPane().add(Box.createHorizontalStrut(50));
    //getContentPane().add(recieptPanel());
    getContentPane().add(Box.createHorizontalGlue());
}


    private JPanel buildMenuPanel (){

    JPanel menuPanel = new JPanel();
    BoxLayout menuLayout = new BoxLayout(menuPanel, BoxLayout.Y_AXIS);
    menuPanel.setLayout(menuLayout);
    getContentPane().add(menuPanel);

    //menuList.addActionListener(
    //new ActionListener()
    {
    //public void actionPerformed(ActionEvent e)
    //{
    //helloPressed();
    //}
    //}
        listModel = new DefaultListModel();
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");

        menuList = new JList(listModel); //data has type Object[]
        menuList.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION);
        menuList.setLayoutOrientation(JList.VERTICAL);
        menuList.setVisibleRowCount(-1);
        menuList.setFixedCellWidth(200);


        JScrollPane listScroller = new JScrollPane(menuList);
        listScroller.setPreferredSize(new Dimension(7, 250));

    menuPanel.add(menuList);

    menuPanel.add(Box.createVerticalStrut(5));
    return menuPanel;
    }

    }


     private JPanel buildOrderPanel (){

    JPanel orderPanel = new JPanel();
    BoxLayout orderLayout = new BoxLayout(orderPanel, BoxLayout.Y_AXIS);
    orderPanel.setLayout(orderLayout);
    getContentPane().add(orderPanel);

    //menuList.addActionListener(
    //new ActionListener()
    //{
    //public void actionPerformed(ActionEvent e)
    //{
    //helloPressed();
    //}
    orderList = new JList(listModel); //data has type Object[]
    orderList.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION);
    orderList.setLayoutOrientation(JList.HORIZONTAL_WRAP);
    orderList.setVisibleRowCount(-1);
    orderList.setFixedCellWidth(200);

    JScrollPane listScroller = new JScrollPane(orderList);
    listScroller.setPreferredSize(new Dimension(250, 80));

    //orderList.setVisible(true); 
    orderPanel.add(orderList);
    //orderPanel.setVisible(true);


    orderPanel.add(Box.createVerticalStrut(5));
    return orderPanel;

    }
     private JPanel buildPayPanel (){

    JPanel payPanel = new JPanel();
    BoxLayout doneLayout = new BoxLayout(payPanel, BoxLayout.Y_AXIS);
    payPanel.setLayout(doneLayout);
    getContentPane().add(payPanel);


    payPanel.add(Box.createVerticalStrut(5));
    listModel = new DefaultListModel();
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");

        menuListDimension = new Dimension (10,10);

        menuList = new JList(listModel); //data has type Object[]
        menuList.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION);
        menuList.setLayoutOrientation(JList.VERTICAL);
        menuList.setVisibleRowCount(50);
        menuList.setFixedCellWidth(300);
        menuList.setDragEnabled(true);
        menuList.setMinimumSize(menuListDimension); 



        JScrollPane listScroller = new JScrollPane(menuList);
        listScroller.setPreferredSize(new Dimension(80, 250));

        payPanel.add(menuList);

        payPanel.add(Box.createVerticalStrut(5));
        getContentPane().add(payPanel);
        JButton payButton = new JButton ("Pay");
        JButton cancelButton = new JButton ("Cancel");

        //menuList.addActionListener(
        //new ActionListener()
        //{
        //public void actionPerformed(ActionEvent e)
        //{
        //helloPressed();
        //}

        payPanel.add(payButton); 
        payPanel.add(cancelButton); 
    return payPanel;


     }


    }

Answer 1

1. Empty JList : JList l = new JList() ;

2. Add a list selection Listener

   firstJList.addSelectionListener(new ListSelectionListener() { public void valueChanged(ListSelectionEvent e) { //add items to your other JList } });

Answer 2

I have commented out lots of the code. I have to say it, please do not get me wrong I do not want to offend any of your skills or anything but this code of yours is one ugly son of ... a code I have seen in a very long time :)

@Swaranga Sarma suggestions are useful. And as stated by this user the JList would show even if empty. You almost had it right, you just added the list wrongly. You were on the right track thought, you have used JScrollPane's but then you should add these to the panel and not the list.

I have decided to use a mouse listener here instead of the suggested by @Swaranga Sarma selection listener because doing so you will have no problem when clicking twice on the same item and adding it only once as it would be if you used the selection listener as it works only on item change.

package test.components;

import java.awt.*;
import java.awt.event.*;


import javax.swing.*;

public class frame extends JFrame
{
    private JList menuList;
    private JList menuList2;
    private JList orderList;
    private JLabel countLabel;
//  private DefaultListModel listModel;
    private Dimension menuListDimension;

    public static void main(String[] args)
    {
        JFrame f = new frame();
        f.setSize(800, 600);
        f.setVisible(true);
    }

    public frame()
    {
        //JFrame frame = new JFrame();
        //frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        buildUI();
    }

    private void buildUI()
    {
        //BoxLayout mainLayout = new BoxLayout(getContentPane(), BoxLayout.X_AXIS);
        GridLayout mainLayout = new GridLayout(1, 5);
        getContentPane().setLayout(mainLayout);

//      getContentPane().add(Box.createHorizontalGlue());
        getContentPane().add(buildMenuPanel());
//      getContentPane().add(Box.createHorizontalStrut(0));
        getContentPane().add(buildOrderPanel());
//      getContentPane().add(Box.createHorizontalStrut(10));
        getContentPane().add(buildPayPanel());
//      getContentPane().add(Box.createHorizontalStrut(50));
//      getContentPane().add(recieptPanel());
//      getContentPane().add(Box.createHorizontalGlue());
    }

    private JPanel buildMenuPanel()
    {
        JPanel menuPanel = new JPanel();
        BoxLayout menuLayout = new BoxLayout(menuPanel, BoxLayout.Y_AXIS);
        menuPanel.setLayout(menuLayout);
        getContentPane().add(menuPanel);

        final DefaultListModel listModel = new DefaultListModel();
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");

        menuList = new JList(listModel); //data has type Object[]
        menuList.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION);
        menuList.setLayoutOrientation(JList.VERTICAL);
        menuList.setVisibleRowCount(50);
        menuList.setFixedCellWidth(150);
        menuList.setBackground(Color.GREEN);

        menuList.addMouseListener(new MouseAdapter()
        {
            @Override
            public void mousePressed(MouseEvent e)
            {
                Object selected = menuList.getSelectedValue();
                System.out.println("menuList.addMouseListener.mousePressed selected=" + selected);
                DefaultListModel dm = (DefaultListModel) orderList.getModel();
                dm.add(orderList.getModel().getSize(), selected);
            }
        });


        JScrollPane listScroller = new JScrollPane(menuList);
        listScroller.setPreferredSize(new Dimension(100, 250));

        menuPanel.add(listScroller);

//          menuPanel.add(Box.createVerticalStrut(5));
        return menuPanel;
    }

    private JPanel buildOrderPanel()
    {
        JPanel orderPanel = new JPanel();
        BoxLayout orderLayout = new BoxLayout(orderPanel, BoxLayout.Y_AXIS);
        orderPanel.setLayout(orderLayout);
        orderList = new JList(new DefaultListModel());//(listModel); //data has type Object[]
        orderList.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION);
        orderList.setLayoutOrientation(JList.HORIZONTAL_WRAP);
        orderList.setVisibleRowCount(50);
        orderList.setFixedCellWidth(150);
        orderList.setBackground(Color.RED);

        JScrollPane listScroller = new JScrollPane(orderList);
        listScroller.setPreferredSize(new Dimension(100, 250));

        //orderList.setVisible(true); 
        orderPanel.add(listScroller);
        //orderPanel.setVisible(true);

//      getContentPane().add(orderPanel);
//      orderPanel.add(Box.createVerticalStrut(5));
        return orderPanel;
    }

    private JPanel buildPayPanel()
    {

        JPanel payPanel = new JPanel();
        BoxLayout doneLayout = new BoxLayout(payPanel, BoxLayout.Y_AXIS);
        payPanel.setLayout(doneLayout);
//      getContentPane().add(payPanel);

//      payPanel.add(Box.createVerticalStrut(5));
        DefaultListModel listModel = new DefaultListModel();
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");
        listModel.addElement("ghjghj");
        listModel.addElement("John Smith");
        listModel.addElement("Kathy Green");

        menuListDimension = new Dimension(10, 10);

        menuList2 = new JList(listModel); //data has type Object[]
        menuList2.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION);
        menuList2.setLayoutOrientation(JList.VERTICAL);
        menuList2.setVisibleRowCount(50);
        menuList2.setFixedCellWidth(150);
        menuList2.setDragEnabled(true);
        menuList2.setBackground(Color.BLUE);
//      menuList2.setMinimumSize(menuListDimension);
        JScrollPane listScroller = new JScrollPane(menuList2);
        listScroller.setPreferredSize(new Dimension(100, 250));

        payPanel.add(listScroller);

//      payPanel.add(Box.createVerticalStrut(5));
//      getContentPane().add(payPanel);
        JButton payButton = new JButton("Pay");
        JButton cancelButton = new JButton("Cancel");

        payPanel.add(payButton);
        payPanel.add(cancelButton);
        return payPanel;
    }
}

Please next time clean the code more :) I really wonder what got me through it. Maybe because I had a similar problem one day, a long time ago, and it was easy to deal with it again? :)

Good luck, Boro.