How do I dynamically add rows in custom DefaultTableModel?

I have subclassed DefaultTableModel so that my table could show values from enum stored in JComboBox. This works fine provided that I add immediately data to this table in constructor. Let me show you what I mean by that.

final List<PageLabel> pageLabels = new ArrayList<>();
// add some data
pageLabels.add(....);
final PageLabelTableModel tableModel = new PageLabelTableModel(pageLabels);

The thing is my application gets data from some text file. Only when this file is processed, the application should add the data the table. So, in other words, I'd like to dynamically add rows to the table. In theory it should be easy. In practice, however, it is not. I wrote a simple method to fill the table:

public void fillTable(final List<PageLabel> labels) {
for (final PageLabel label : labels) {
final Vector<PageLabel> rowData = new Vector<>();
rowData.add(label);
tableModel.addRow(rowData);
}
}

It fails with the exception:

Exception in thread "Thread-1" java.lang.ArrayIndexOutOfBoundsException: 0 >= 0
at java.base/java.util.Vector.elementAt(Vector.java:466)
at java.desktop/javax.swing.table.DefaultTableModel.justifyRows(DefaultTableModel.java:278)
at java.desktop/javax.swing.table.DefaultTableModel.insertRow(DefaultTableModel.java:382)
at java.desktop/javax.swing.table.DefaultTableModel.addRow(DefaultTableModel.java:357)

Why is that? Here's my custom table model class:

// the code heavily borrows from
// https://www.codejava.net/java-se/swing/how-to-create-jcombobox-cell-editor-for-jtable
public class PageLabelTableModel extends DefaultTableModel {
private static final String[] columnNames = { "Label", "Start page", "Style" };
private final List<PageLabel> pageLabels = new ArrayList<>();
public PageLabelTableModel() {
super(columnNames, 0);
}
@Override
public Class<?> getColumnClass(final int column) {
return getValueAt(0, column).getClass();
}
@Override
public int getRowCount() {
return pageLabels != null ? pageLabels.size() : 0;
}
@Override
public int getColumnCount() {
return columnNames.length;
}
@Override
public String getColumnName(final int column) {
return columnNames[column];
}
@Override
public boolean isCellEditable(final int rowIndex, final int columnIndex) {
return columnIndex >= 0;
}
@Override
public Object getValueAt(final int rowIndex, final int columnIndex) {
final PageLabel pageLabel = pageLabels.get(rowIndex);
final Object returnValue;
switch (columnIndex) {
case 0 -> returnValue = pageLabel.label();
case 1 -> returnValue = pageLabel.startPage();
case 2 -> returnValue = pageLabel.style();
default -> throw new IllegalArgumentException(
String.format("Column index %d not found!", columnIndex)
);
}
return returnValue;
}
@Override
public void setValueAt(final Object value, final int rowIndex, final int columnIndex) {
final PageLabel pageLabel = pageLabels.get(rowIndex);
switch (columnIndex) {
case 0 -> pageLabel.label((String) value);
case 1 -> pageLabel.startPage((int) value);
case 2 -> pageLabel.style((LabelStyle) value);
default -> throw new IllegalArgumentException(
String.format("Column index %d not found!", columnIndex)
);
}
}
}

As per comment by @Abra I provide the code for PageLabel class:

public class PageLabel {
private String label;
private int startPage;
private LabelStyle style;
// no-args, all-args, getters/setters
// omitted for brevity
}

Below is enum used by the above-mentioned class:

public enum LabelStyle {
DECIMAL("Decimal"),
ROMAN_LOWER("Roman lower"),
ROMAN_UPPER("Roman upper"),
LETTER_UPPPER("Letters upper"),
LETTER_LOWER("Letters lower"),
NONE("None");
private final String style;
LabelStyle(final String style) {
this.style = style;
}
}

Hopefully you can build on this minimal refactor of your PageLabelTableModel class.

import java.util.ArrayList;
import java.util.List;

import javax.swing.table.AbstractTableModel;

public class PageLabelTableModel extends AbstractTableModel {
    private static final String[] columnNames = { "Label", "Start page", "Style" };
    private final List<PageLabel> pageLabels;

    public PageLabelTableModel() {
        this(new ArrayList<>());
    }

    public PageLabelTableModel(List<PageLabel> labels) {
        pageLabels = labels;
    }

    public void addRow(PageLabel label) {
        pageLabels.add(label);
        int count = getRowCount();
        fireTableRowsInserted(count, count);
    }

    @Override
    public int getRowCount() {
        return pageLabels == null ? 0 : pageLabels.size();
    }

    public Class<?> getColumnClass(int columnIndex) {
        Class<?> theClass;
        switch (columnIndex) {
            case 0:
                theClass = String.class;
                break;
            case 1:
                theClass = Number.class;
                break;
            case 2:
                theClass = LabelStyle.class;
                break;
            default:
                theClass = Object.class;
        }
        return theClass;
    }

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

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

    @Override
    public Object getValueAt(int rowIndex, int columnIndex) {
        Object value;
        PageLabel pageLabel = pageLabels.get(rowIndex);
        switch (columnIndex) {
            case 0:
                value = pageLabel.getLabel();
                break;
            case 1:
                value = Integer.valueOf(pageLabel.getStartPage());
                break;
            case 2:
                value = pageLabel.getStyle();
                break;
            default:
                value = null;
        }
        return value;
    }

    @Override
    public boolean isCellEditable(final int rowIndex, final int columnIndex) {
       return columnIndex >= 0;
    }
}

• Classes that extend AbstractTableModel must implement the following three methods:
  1. getRowCount
  2. getColumnCount
  3. getValueAt
• It is also recommended to override other AbstractTableModel methods, including:
  1. getColumnName
     (Look at code of that method in class AbstractTableModel to understand why.)
  2. getColumnClass
     (To make use of the default renderers. Refer to How to Use Tables for more details.)
  3. isCellEditable
     (But you have already overridden this.)
• Note in the addRow method, the call to fireTableRowsInserted. This is to notify the JTable class that the data in the model has changed. Again, refer to How to Use Tables for more details.

Also, I added a toString method to LabelStyle:

public enum LabelStyle {
    DECIMAL("Decimal"),
    ROMAN_LOWER("Roman lower"),
    ROMAN_UPPER("Roman upper"),
    LETTER_UPPPER("Letters upper"),
    LETTER_LOWER("Letters lower"),
    NONE("None");

    private final String style;

    LabelStyle(final String style) {
       this.style = style;
    }

    public String toString() {
        return style;
    }
}