JTable doesn't want to show content

Question

I'm trying to show table from JSONArray. but the result never show up. The table already show up with right column name by calling this initTable() method. The initTable() is as follow:

private void initTable() {
    contentPane.removeAll();

    PrintTableModel tblModel = new PrintTableModel();

    DefaultTableColumnModel columns = new DefaultTableColumnModel();
    TableColumn c;

    c = new TableColumn();
    c.setHeaderValue(columnNames[0]);
    columns.addColumn(c);

    c = new TableColumn();
    c.setHeaderValue(columnNames[1]);
    columns.addColumn(c);

    c = new TableColumn();
    c.setHeaderValue(columnNames[2]);
    columns.addColumn(c);

    c = new TableColumn();
    c.setHeaderValue(columnNames[3]);
    columns.addColumn(c);

    listTable = new JTable(tblModel, columns);
    listTable.getTableHeader().setReorderingAllowed(false);

    JScrollPane scrollPane = new JScrollPane();
    scrollPane.add(listTable);
    scrollPane.setViewportView(listTable);
    contentPane.add(scrollPane, BorderLayout.CENTER);       
}

And I'm calling the refresh table from a thread like this:

public class RetrievePrintRequest extends Thread {
    private boolean speedUp = false;

    public void run() {
        if (loginId == 0)
            return;

        try {
            String token = generateLink("prc_admin_id=" + loginId);
            do {
                JSONArray jsonresult = readJsonFromUrl(BASE_URL + "ajax/get_latest_print?code=" + token);

                // looping through All elements
                // list holding row data
                List<PrintModel> printList = new ArrayList<PrintModel>();
                for (int i = 0; i < jsonresult.length(); i++) {
                    JSONObject c = jsonresult.getJSONObject(i);

                    // Storing each json item in variable
                    int printId = c.getInt("print_id");
                    String bookingCode = c.getString("booking_code");
                    long startDate = c.getLong("start_date");
                    String patientName = c.getString("patient_name");
                    String doctorName = c.getString("doc_name");

                    PrintModel printModel = new PrintModel(
                            printId, bookingCode, patientName, doctorName, new Date(startDate));
                    // add rest of the json data to NodePOJO class

                    System.out.println(printId + ";" + bookingCode + ";" + startDate + ";" + patientName + ";" + doctorName);
                    // the object to list
                    printList.add(printModel);
                }
                PrintTableModel printModel = (PrintTableModel) listTable.getModel();
                printModel.refresh(printList); //<--- I expect this to refresh the table content
                Thread.sleep(!speedUp ? 10000 : 60000);
            } while(true);
        } catch (JSONException | IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

And this is the refresh method inside TableModel (Add the whole PrintTableModel class)

protected class PrintTableModel extends DefaultTableModel {
        private List<PrintModel> listData;

        public void refresh(List<PrintModel> data) {
            listData = data; // <== refresh with new List and call fireTableDataChanged
            fireTableDataChanged();
        }

        public Object getValueAt(int row, int column) {
            Object result = null;

            PrintModel model = (PrintModel)listData.get(row);
            switch (column)
            {
                case 0:
                    result = model.getBookingCode();
                    break;
                case 1:
                    result = SDF.format(model.getAppointmentDate());
                    break;
                case 2:
                    result = model.getPatientName();
                    break;
                case 3:
                    result = model.getDoctorName();
                    break;      
            }
            return result;
        }

        public Class getColumnClass(int column) {
            switch (column)
            {
                case 0:
                    return String.class;
                case 1:
                    return String.class;
                case 2:
                    return String.class;            
                case 3:
                    return String.class;
            }
            return null;
        }

Anyone can spot my error? Many thanks.

Answer 1

You are updating UI from a Thread that is not synchronized with the Event Dispatch Thread (EDT):

Swing event handling code runs on a special thread known as the event dispatch thread. Most code that invokes Swing methods also runs on this thread. This is necessary because most Swing object methods are not "thread safe": invoking them from multiple threads risks thread interference or memory consistency errors

Swing is not thread safe and so you need to update the UI by using SwingUtilities.invokeLater.

From the documentation on SwingUtilities.invokeLater:

Causes doRun.run() to be executed asynchronously on the AWT event dispatching thread. This will happen after all pending AWT events have been processed. This method should be used when an application thread needs to update the GUI.

---

PS: Use this way of adding the table to the content pane:

contentPane.add(new JScrollPane(listTable), BorderLayout.CENTER);

Answer 2

To add to what TT. has already said...

For iteration of the for-loop, you do this...

    PrintModel printModel = new PrintModel(printId, bookingCode, patientName, doctorName, new Date(startDate));
    // add rest of the json data to NodePOJO class

    System.out.println(printId + ";" + bookingCode + ";" + startDate + ";" + patientName + ";" + doctorName);
    // the object to list
    printList.add(printModel);
}

After you processed each "row", you do this...

PrintTableModel printModel = (PrintTableModel) listTable.getModel();
printModel.refresh(printList); //<--- I expect this to refresh the table content

The question here is, what relationship does the PrintModel you make in the for-loop have to the one which you try and refresh?

Instead, you should either be creating a new instance of PrintTableModel BEFORE the start of the for-loop, adding each row of data to this instance of PrintTableModel and then (after synchornising the calling to the EDT) applying this instance of the PrintTableModel to the JTable

OR

Using a SwingWorker, publish each row of data and adding it the current instance of PrintTableModel (from the JTable) when you process it.

See Concurrency in Java and Worker Threads and SwingWorker for more details

Answer 3

The Answer: It didn't work because DefaultTableModel has it's own Vector data, and creating new one didn't affected when calling fireTableDataChanged(). So, I guess DefaultTableModel not design to be extended, but to be used as standard TableModel. Java provides AbstractTableModel for extended purposes.

So, this is the new code that extended from AbstractTableModel:

protected class PrintTableModel extends AbstractTableModel {
    private List<PrintModel> listData = new ArrayList<PrintModel>();
    protected String[] columnNames;

    public int getRowCount() {
        return listData.size();
    }

    public void setColumnNames(String[] columnNames) {
        this.columnNames = columnNames;
    }

    public String getColumnName(int column) {
        return columnNames[column];
    }

    public int getColumnCount() {
        return columnNames.length;
    }

    public void add(Object obj) {
        listData.add(0, (PrintModel)obj);
        fireTableRowsInserted(listData.size() - 1, listData.size() - 1);
    }

    public void update(Object obj, int row) {
        listData.set(row, (PrintModel)obj);
        fireTableRowsUpdated(row, row);
    }

    public void remove(int row) {
        listData.remove(row);
        fireTableRowsDeleted(row, row);
    }

    public Object getObjectAt(int row) {
        return listData.get(row);
    }

    public void refresh(List<PrintModel> data) {
        listData = data;
        fireTableDataChanged();
    }

    public Object getValueAt(int row, int column) {
        Object result = null;

        PrintModel model = (PrintModel)listData.get(row);
        switch (column)
        {
            case 0:
                result = model.getBookingCode();
                break;
            case 1:
                result = SDF.format(model.getAppointmentDate());
                break;
            case 2:
                result = model.getPatientName();
                break;
            case 3:
                result = model.getDoctorName();
                break;  
            case 4:
                result = "Print";
                break;                  
        }
        return result;
    }

    public Class getColumnClass(int column) {
        switch (column)
        {
            case 0:
                return String.class;
            case 1:
                return String.class;
            case 2:
                return String.class;            
            case 3:
                return String.class;
            case 4:
                return String.class;                    
        }
        return null;
    }       
}