How to Validate Non-Positive Integer Input in JTable Cells?

Invalid Input Validation in JTable Cells

Question:

Consider a JTable where a column's class type is specified as Integer using the getColumnClass() method. Swing automatically marks and rejects invalid inputs (e.g., double values). However, a custom validation for non-positive integer input (negative or zero) is desired, mimicking the default behavior for invalid integer inputs.

Answer:

Unlike Swing's default checks, which use introspection to detect exceptions, a custom editor can be employed for specific validation. For instance, PositiveIntegerCellEditor can be created as a subclass of DefaultCellEditor to accomplish the task.

In stopCellEditing() method, an attempt to convert the input to an Integer is made. If the value is non-positive, a NumberFormatException is thrown, causing the textField to be outlined in red, indicating an invalid input.

<code class="java">private static class PositiveIntegerCellEditor extends DefaultCellEditor {

    private static final Border red = new LineBorder(Color.red);
    private static final Border black = new LineBorder(Color.black);
    private JTextField textField;

    public PositiveIntegerCellEditor(JTextField textField) {
        super(textField);
        this.textField = textField;
        this.textField.setHorizontalAlignment(JTextField.RIGHT);
    }

    @Override
    public boolean stopCellEditing() {
        try {
            int v = Integer.valueOf(textField.getText());
            if (v < 0) {
                throw new NumberFormatException();
            }
        } catch (NumberFormatException e) {
            textField.setBorder(red);
            return false;
        }
        return super.stopCellEditing();
    }

    @Override
    public Component getTableCellEditorComponent(JTable table,
        Object value, boolean isSelected, int row, int column) {
        textField.setBorder(black);
        return super.getTableCellEditorComponent(
            table, value, isSelected, row, column);
    }
}</code>

When a cell with an invalid input is clicked, the PositiveIntegerCellEditor will be activated, and upon exiting edit mode (e.g., by pressing Enter or Tab), the stopCellEditing() method will attempt to convert the input. If the conversion fails (i.e., the input is non-positive), the textField border will be set to red, and the focus will remain on the cell.

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