Swing - JTable and DefaultTableModel references always return null

Question

I'm writing an app that reads a series of strings from a virtual COM port and then displays those strings in a table so the user can edit them and export back out the COM port. I am using Swing with JTable and DefaultTableModel. I can initialize the table OK and display dummy data, but am unable to use fireTableDataChanged() to update the table data with the values read from the serial port.

public class SwingMain extends JFrame {
    ...
    private JScrollPane lensListScroller;
    private JPanel listPane;
    private static JTable workListTable;
    private static DefaultTableModel workListModel;
    private static String[] columnNames = {"Manufacturer", "Series", "Focal Length", "Status"};
    static Object[][] lensTableData;
    ...

    public SwingMain() {
        ...
        // dummy data to populate the table at the beginning
        Object[][] lensTableData = {{"Angenieux", "Optimo", "24-290mm", "Calibrated: F | Mylist: A"}};
        DefaultTableModel workListModel = new DefaultTableModel(lensTableData, columnNames);
        JTable workListTable = new JTable(workListModel);

        // Scroll pane for Lens Work List
        JScrollPane lensListScroller = new JScrollPane(workListTable);

        JPanel listPane = new JPanel();
        listPane.setLayout(new BoxLayout(listPane, BoxLayout.PAGE_AXIS));
        JLabel label = new JLabel("Work List");
    }
    ...
}

That all works fine for showing the table initially. I run into problems when I try to add the imported data to the DefaultTableModel workListModel:

public class SwingMain extends JFrame {
    ...
    private static void receiveLensData(String text) throws SerialPortException {
        System.out.println("receiveLensData: " + text);
        if (!isConnected) {
            if (text.contains("Hand")) {
                System.out.println("Hand detected");
                timer.cancel();
            }
        }
        else {
            if (transfer) {
                if (!startLensRx) {
                        ...
                        lensTableData = new Object[numLenses][4];
                } else {
                    if (text.contains(EOTStr)) {
                        System.out.println("EOT detected");
                        serialPort.writeBytes(ACK_SYN);
                        transfer = false;
                        startLensRx = false;
                        currentLens = 0;
                        progressBar.setVisible(false);
                        addLensesToWorkList(); // <-- calling the function to populate the table
                    } else {
                        System.out.println("Lens " + currentLens + " of " + numLenses + ": " + text);
                        lensArray.add(text);
                        progressBar.setValue(currentLens);
                        currentLens += 1;
                        serialPort.writeBytes(ACK);
                    }

                }
            }
        }
    }

    private static void addLensesToWorkList() {
        for (int i=0; i < lensArray.size(); i++) {
            // add the imported string to the Object[][] that the table model was declared with
            lensTableData[i] = parseLensLine(lensArray.get(i));
        }

        // after updating lensTableData, I want to tell the table model that the dataset has changed. 
        // But workListModel and workListTable always are null:
        SwingUtilities.invokeLater(new Runnable(){public void run(){
            workListModel.fireTableDataChanged();  // <-NullPointerException here
        }});
    }
}

I can tell that the Object[][] lensTableData is getting populated correctly, but I'm unable to reference the table (workListTable) or its model (workListModel) since they always return null when I try to reference them from within addLensesToWorkList() method.

I imagine I'm just missing something in the initial declaration of the table and/or model. Or do I need to create a new table/model after importing the data and then add that table to my JScrollPane? I'm new to Java dev for desktop. Thanks in advance for any advice :)

Please show code where you are calling `addLensesToWorkList()` — SomeDude, Jun 26 '17 at 19:28
You would debug this as you would any other NullPointerException. Please read the duplicate as it will show you the steps that you need to follow. — Hovercraft Full Of Eels, Jun 26 '17 at 19:40
You're shadowing the workListModel variable. Don't do that. Don't re-declare it in the constructor. i.e., don't do `Foo foo = new Foo();` in the constructor or method but rather `foo = new Foo();` -- see the difference? — Hovercraft Full Of Eels, Jun 26 '17 at 19:47
For similar error see [this question and answer](https://stackoverflow.com/a/34979808/522444) — Hovercraft Full Of Eels, Jun 26 '17 at 20:43
Thanks for those pointers. What should I be declaring `static`? If I don't declare `workListTable` and `workListModel` as `static`, I get an error `Cannot make a static reference to the non-static field workListModel` — Matt Davis, Jun 26 '17 at 20:54
Removing the variable shadowing and declaring `workListModel` and `workListTable` as `public static` seems to have worked. Should I be declaring those `static`? — Matt Davis, Jun 26 '17 at 21:28
No, none of those fields should be static. You may wish to study a decent book or chapter on OOPs as it applies to Java programming since this concept is too key and too intrinsic to Java programming to ignore. — Hovercraft Full Of Eels, Jun 27 '17 at 11:09
`"Cannot make a static reference to the non-static field workListModel"` -- especially if you don't see that you're fixing this problem the exact wrong way. — Hovercraft Full Of Eels, Jun 27 '17 at 11:09

Swing - JTable and DefaultTableModel references always return null

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