JComboBox show value

Question

Need help with JComboBox component. I've load data from MySQL database and write this data into combo. I use four combo boxes with ItemListener. When one combo box change all children combo boxes reload data from database. First and two works fine but third and four don't show value normal, but good value is there. Only I don't show it. When I select empty field in combo box after then I see good result.

Source code:

public class Vyhladat extends Okno {
    private static final long serialVersionUID = 1L;
    JComboBox nominalBOX,statBOX,podpisBOX,tlacDoskaBOX;
    Font sherif = new Font("Sherif",Font.BOLD,20);
    Font normal = new Font("Sherif",Font.PLAIN,20);
    JFrame uh = new JFrame();
            private String adresa="jdbc:mysql://localhost:3306/jarodb";
    private String meno="JKARAK";
    private String heslo="bankovka";
    String nominal,stat,podpis,tlacDoska,statH;
    private String nominalSQL = "SELECT DISTINCT(nominal) FROM prehlad";
    private String statSQL = "SELECT DISTINCT(concat(stat,'/',seria)) FROM prehlad WHERE nominal=? ORDER BY stat";
    private String podpisSQL = "SELECT DISTINCT(podpis) FROM prehlad WHERE nominal=? AND stat=? ";
    private String tlacDoskaSQL = "SELECT DISTINCT(doska) FROM prehlad WHERE nominal=? AND stat=? AND podpis=? ";

    Vector nominalV=new Vector();
    Vector statV=new Vector();
    Vector podpisV=new Vector();
    Vector tlacDoskaV=new Vector();

    Vyhladat()
    {

        vlozPopis(nominalLAB,"NOMIN\u00C1L EUROBANKOVKY:   ",0,0,sherif);
        vlozPopis(statLAB,"\u0160T\u00C1T/S\u00C9RIA:",0,1,sherif);
        vlozPopis(podpisLAB,"PODPIS:",0,2,sherif);
        vlozPopis(tlacDoskaLAB,"TLA\u010COV\u00C1 DOSKA:",0,3,sherif);

        gbc.gridx=1;
        gbc.gridy=0;
        nacitajVyber(nominalSQL,nominalBOX,nominalV,false,false,false);
        nominalBOX = new JComboBox(nominalV);

        nominalBOX.addItemListener(new ItemListener()
        {
            public void itemStateChanged(ItemEvent e) 
            {
                nominal = (String)nominalBOX.getSelectedItem();

                if(nominal!=" ")
                {
                    nacitajVyber(statSQL,statBOX,statV,true,false,false);
                }
                else{
                    statBOX.removeAllItems();
                    podpisBOX.removeAllItems();
                    tlacDoskaBOX.removeAllItems();
                    }
            }   
        });
        nominalBOX.setPrototypeDisplayValue("500");
        nominalBOX.setFont(normal);
        nominalBOX.setSelectedIndex(0);
        nominalBOX.setToolTipText("Vyber z mo\u017Enost\u00ED nomin\u00E1lu bankoviek 5,10,20,50.");
        add(nominalBOX,gbc);

        gbc.gridx=1;
        gbc.gridy=1;
        statV.add(" ");
        statBOX= new JComboBox(statV);
        statBOX.addItemListener(new ItemListener()
        {
            public void itemStateChanged(ItemEvent e) 
            {
                stat = (String)statBOX.getSelectedItem();

                if(stat!=null)
                {
                    String [] statM= stat.split("/");
                    statH = statM[0];
                }

                if(stat!=" " & stat!=null)
                {
                    nacitajVyber(podpisSQL,podpisBOX,podpisV,false,true,false);
                }
                else{
                  podpisBOX.removeAllItems();
                  tlacDoskaBOX.removeAllItems();
                    }
            }   
        });
        statBOX.setPrototypeDisplayValue("Portugalsko/E");
        statBOX.setFont(normal);
        statBOX.setSelectedIndex(0);
        statBOX.setToolTipText("Vyber z mo\u017Enost\u00ED \u0161t\u00E1t/s\u00E9riu.");
        add(statBOX,gbc);

        gbc.gridx=1;
        gbc.gridy=2;
        podpisV.add(" ");
        podpisBOX = new JComboBox(podpisV);
        podpisBOX.addItemListener(new ItemListener()
        {
            public void itemStateChanged(ItemEvent e) 
            {
                podpis = (String)podpisBOX.getSelectedItem();

                if(podpis!=" " & podpis!=null)
                {
                    nacitajVyber(tlacDoskaSQL,tlacDoskaBOX,tlacDoskaV,false,false,true);
                }
                else{
                  tlacDoskaBOX.removeAllItems();
                    }
            }   
        });
        podpisBOX.setPrototypeDisplayValue("Jean-Claude Trichet ");
        podpisBOX.setFont(normal);
        podpisBOX.setSelectedIndex(0);
        podpisBOX.setToolTipText("Vyber z mo\u017Enost\u00ED troch podpisov.");
        add(podpisBOX,gbc);

        gbc.gridx=1;
        gbc.gridy=3;
        tlacDoskaV.add(" ");
        tlacDoskaBOX = new JComboBox(tlacDoskaV);

        tlacDoskaBOX.addItemListener(new ItemListener()
        {
            public void itemStateChanged(ItemEvent e) 
            {
                tlacDoska = (String)tlacDoskaBOX.getSelectedItem();

                if((nominal!=" " & nominal!=null) & (statH!=" " & statH!=null) & (podpis!=" " & podpis!=null) & (tlacDoska!=" " & tlacDoska!=null))
                {
                    zobraz.setEnabled(true);
                }

            }   
        });
        tlacDoskaBOX.setPrototypeDisplayValue("E010");
        tlacDoskaBOX.setFont(normal);
        tlacDoskaBOX.setSelectedIndex(0);
        tlacDoskaBOX.setToolTipText("Vyber z mo\u017Enost\u00ED tla\u010Dov\u00FDch dosiek.");
        add(tlacDoskaBOX,gbc);
}
private void nacitajVyber(String sqlDotaz, JComboBox chr,Vector v,
        boolean jedna,boolean dva, boolean tri)
{
    try
    {
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection(adresa,meno,heslo);
        PreparedStatement stmt = conn.prepareStatement(sqlDotaz);
        if(jedna==true)
            {
            chr.removeAllItems();
        stmt.setString(1, nominal);
        }
        if(dva==true)
        {
                    chr.removeAllItems();
            stmt.setString(1, nominal);
            stmt.setString(2, statH);
        }
        if(tri==true)
        {
                    chr.removeAllItems();
            stmt.setString(1, nominal);
            stmt.setString(2, statH);
            stmt.setString(3, podpis);
        }

        ResultSet rs = stmt.executeQuery();
           v.addElement(" ");
            while (rs.next())
                {v.addElement(rs.getString(1).trim());
            System.out.println(rs.getString(1));}



        validate();
        rs.close();
        stmt.close();
        conn.close();
    }
    catch(Exception e){
        JOptionPane.showMessageDialog(uh,e.toString(),
                "Chyba pripojenia",
                JOptionPane.ERROR_MESSAGE);
    }

}
}

Answer 1

• JComboBox doesn't know somehow then underlaying Vector is changed, have to reinitialize this array for JComboBox on the fly, but this is wrong way,

• for any changes on the runtime to use XxxComboBoxModel for storing Items for JComboBox

• for JDBC or FileIO there could be Concurency issue, Swing JComponents required to all updates (in this case JComboBox and its XxxComboBoxModel) must be done on EDT

• invoke Database event from the Runnable#Thread or SwingWorker, redirect this (potentionally) hard and long running task to the Workers Thread, otherwise Swing GUi will be freeze or unresponsive (for mouse and key events) untill JDBC ended

• SwingWorkers methods publish(), process() and done() quite good quaranteed that all output wil be done on EDT

for example

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;

public class ComboBoxTwo extends JFrame implements ActionListener, ItemListener {

    private static final long serialVersionUID = 1L;
    private JComboBox mainComboBox;
    private JComboBox subComboBox;
    private Hashtable<Object, Object> subItems = new Hashtable<Object, Object>();

    public ComboBoxTwo() {
        String[] items = {"Select Item", "Color", "Shape", "Fruit"};
        mainComboBox = new JComboBox(items);
        mainComboBox.addActionListener(this);
        mainComboBox.addItemListener(this);
        //prevent action events from being fired when the up/down arrow keys are used
        //mainComboBox.putClientProperty("JComboBox.isTableCellEditor", Boolean.TRUE);
        getContentPane().add(mainComboBox, BorderLayout.WEST);
        subComboBox = new JComboBox();//  Create sub combo box with multiple models
        subComboBox.setPrototypeDisplayValue("XXXXXXXXXX"); // JDK1.4
        subComboBox.addItemListener(this);
        getContentPane().add(subComboBox, BorderLayout.EAST);
        String[] subItems1 = {"Select Color", "Red", "Blue", "Green"};
        subItems.put(items[1], subItems1);
        String[] subItems2 = {"Select Shape", "Circle", "Square", "Triangle"};
        subItems.put(items[2], subItems2);
        String[] subItems3 = {"Select Fruit", "Apple", "Orange", "Banana"};
        subItems.put(items[3], subItems3);
//      mainComboBox.setSelectedIndex(1);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        String item = (String) mainComboBox.getSelectedItem();
        Object o = subItems.get(item);
        if (o == null) {
            subComboBox.setModel(new DefaultComboBoxModel());
        } else {
            subComboBox.setModel(new DefaultComboBoxModel((String[]) o));
        }
    }

    @Override
    public void itemStateChanged(ItemEvent e) {
        if (e.getStateChange() == ItemEvent.SELECTED) {
            if (e.getSource() == mainComboBox) {
                if (mainComboBox.getSelectedIndex() != 0) {
                    FirstDialog firstDialog = new FirstDialog(ComboBoxTwo.this,
                            mainComboBox.getSelectedItem().toString(), "Please wait,  Searching for ..... ");
                }
            } 
        }
    }

    private class FirstDialog extends JDialog { //sipmle simulation of JDBC events, by using Swing Timer

        private static final long serialVersionUID = 1L;

        FirstDialog(final Frame parent, String winTitle, String msgString) {
            super(parent, winTitle);
            setModalityType(Dialog.ModalityType.APPLICATION_MODAL);
            JLabel myLabel = new JLabel(msgString);
            JButton bNext = new JButton("Stop Processes");
            add(myLabel, BorderLayout.CENTER);
            add(bNext, BorderLayout.SOUTH);
            bNext.addActionListener(new ActionListener() {

                @Override
                public void actionPerformed(ActionEvent evt) {
                    setVisible(false);
                }
            });
            javax.swing.Timer t = new javax.swing.Timer(1000, new ActionListener() {

                @Override
                public void actionPerformed(ActionEvent e) {
                    setVisible(false);
                }
            });
            t.setRepeats(false);
            t.start();
            setLocationRelativeTo(parent);
            setSize(new Dimension(400, 100));
            setVisible(true);
        }
    }

    public static void main(String[] args) {
        JFrame frame = new ComboBoxTwo();
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

Answer 2

The GUI probably can't redraw properly. You are doing all of your hard work on the Event Dispatch Thread. This thread calls your itemStateChanged. But this thread is also responsible for redrawing the GUI. You are stopping it from doing that, because you are making it do your hard work in the database.

Instead, you can use a different thread to do your hard work.

    public void itemStateChanged(ItemEvent e) 
    {
        new Thread(new Runnable() {
            public void run() {
                .... your code...
            }
        }).start();
    }

Or take a look at SwingWorker, which does this in a nicer way.

Also, itemStateChanged could be called twice for each selection - this might be causing you problems. Use "e.getStateChange()" to check what TYPE of event you just received. You should receive a selected and an unselected (from the old item).