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Swing Chapter 18. (Advanced topics) Tables. Easy for reading, Click here!

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Swing Chapter 18. (Advanced topics) Tables. Easy for reading, Click here!

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18.8  Custom models, editors, and renderers

In constructing our StocksTable application we talked mostly about displaying and retrieving data in JTable. In this section we will construct a basic expense report application, and in doing so we will concentrate on table cell editing. We will also see how to implement dynamic addition and removal of table rows.

The editing of data generally follows this scheme:

Create an instance of the TableCellEditor interface. We can use the DefaultCellEditor class or implement our own. The DefaultCellEditor class takes a GUI component as a parameter to its constructor: JTextField, JCheckBox or JComboBox. This component will be used for editing.

If we are developing a custom editor, we need to implement the getTableCellEditorComponent() method which will be called each time a cell is about to be edited.

In our table model we need to implement the setValueAt(Object value, int nRow, int nCol) method which will be called to change a value in the table when an edit ends. This is where we can perform any necessary data processing and validation.

The data model for this example is designed as follows (where each row represents a column in our JTable):

Name                      Type                       Description

Date                        String                Date of expense

Amount                 Double                Amount of expense

Category                Integer             Category from pre-defined list

Approved              Boolean             Sign of approval for this expense.

Description           String                Brief description

Figure 18.7 An expense report app illustrating custom cell editing, rendering, and row addition/removal.

<<file figure18-7.gif>>

Note: Since the only math that is done with our "Amount" values is addition, using Doubles is fine. However, in more professional implementations we may need to use rounding techniques or a custom renderer to remove unneccessary fractional amounts.

The Code: ExpenseReport.java

see \Chapter18\7

import java.awt.*;

import java.awt.event.*;

import java.util.*;

import java.io.*;

import java.text.SimpleDateFormat;

import javax.swing.*;

import javax.swing.border.*;

import javax.swing.event.*;

import javax.swing.table.*;

public class ExpenseReport extends JFrame


  protected JTable m_table;

  protected ExpenseReportData m_data;

  protected JLabel m_title;

  public ExpenseReport() {

    super("Expense Report");

    setSize(570, 200);

    m_data = new ExpenseReportData(this);

    m_table = new JTable();




    for (int k = 0; k < ExpenseReportData.m_columns.length; k++) {

      TableCellRenderer renderer;

      if (k==ExpenseReportData.COL_APPROVED)

        renderer = new CheckCellRenderer();

      else {

        DefaultTableCellRenderer textRenderer =

          new DefaultTableCellRenderer();



        renderer = textRenderer;


      TableCellEditor editor;

      if (k==ExpenseReportData.COL_CATEGORY)

        editor = new DefaultCellEditor(new JComboBox(


      else if (k==ExpenseReportData.COL_APPROVED)

        editor = new DefaultCellEditor(new JCheckBox());


        editor = new DefaultCellEditor(new JTextField());

      TableColumn column = new TableColumn(k,


          renderer, editor);



    JTableHeader header = m_table.getTableHeader();


    JScrollPane ps = new JScrollPane();

    ps.setSize(550, 150);


    getContentPane().add(ps, BorderLayout.CENTER);

    JPanel p = new JPanel();

    p.setLayout(new BoxLayout(p, BoxLayout.X_AXIS));

    ImageIcon penny = new ImageIcon("penny.gif");

    m_title = new JLabel("Total: $",

      penny, JButton.LEFT);





    JButton bt = new JButton("Insert before");



    ActionListener lst = new ActionListener() {

      public void actionPerformed(ActionEvent e) {

        int row = m_table.getSelectedRow();


        m_table.tableChanged(new TableModelEvent(

          m_data, row, row, TableModelEvent.ALL_COLUMNS,







    bt = new JButton("Insert after");



    lst = new ActionListener() {

      public void actionPerformed(ActionEvent e) {

        int row = m_table.getSelectedRow();


        m_table.tableChanged(new TableModelEvent(

          m_data, row+1, row+1, TableModelEvent.ALL_COLUMNS,







    bt = new JButton("Delete row");



    lst = new ActionListener() {

      public void actionPerformed(ActionEvent e) {

        int row = m_table.getSelectedRow();

        if (m_data.delete(row)) {

          m_table.tableChanged(new TableModelEvent(

            m_data, row, row, TableModelEvent.ALL_COLUMNS,









    getContentPane().add(p, BorderLayout.SOUTH);


    WindowListener wndCloser = new WindowAdapter() {

      public void windowClosing(WindowEvent e) {







  public void calcTotal() {

    double total = 0;

    for (int k=0; k<m_data.getRowCount(); k++) {

      Double amount = (Double)m_data.getValueAt(k,


      total += amount.doubleValue();


    m_title.setText("Total: $"+total);


  public static void main(String argv[]) {

    new ExpenseReport();



class CheckCellRenderer extends JCheckBox implements TableCellRenderer


  protected static Border m_noFocusBorder;

  public CheckCellRenderer() {


    m_noFocusBorder = new EmptyBorder(1, 2, 1, 2);




  public Component getTableCellRendererComponent(JTable table,

   Object value, boolean isSelected, boolean hasFocus,

   int row, int column)


    if (value instanceof Boolean) {

      Boolean b = (Boolean)value;



    setBackground(isSelected && !hasFocus ?

      table.getSelectionBackground() : table.getBackground());

    setForeground(isSelected && !hasFocus ?

      table.getSelectionForeground() : table.getForeground());


    setBorder(hasFocus ? UIManager.getBorder(

      "Table.focusCellHighlightBorder") : m_noFocusBorder);

    return this;



class ExpenseData


  public Date    m_date;

  public Double  m_amount;

  public Integer m_category;

  public Boolean m_approved;

  public String  m_description;

  public ExpenseData() {

    m_date = new Date();

    m_amount = new Double(0);

    m_category = new Integer(1);

    m_approved = new Boolean(false);

    m_description = "";


  public ExpenseData(Date date, double amount, int category,

   boolean approved, String description)


    m_date = date;

    m_amount = new Double(amount);

    m_category = new Integer(category);

    m_approved = new Boolean(approved);

    m_description = description;



class ColumnData


  public String  m_title;

  int m_width;

  int m_alignment;

  public ColumnData(String title, int width, int alignment) {

    m_title = title;

    m_width = width;

    m_alignment = alignment;



class ExpenseReportData extends AbstractTableModel


  public static final ColumnData m_columns[] = {

    new ColumnData( "Date", 80, JLabel.LEFT ),

    new ColumnData( "Amount", 80, JLabel.RIGHT ),

    new ColumnData( "Category", 130, JLabel.LEFT ),

    new ColumnData( "Approved", 80, JLabel.LEFT ),

    new ColumnData( "Description", 180, JLabel.LEFT )


  public static final int COL_DATE = 0;

  public static final int COL_AMOUNT = 1;

  public static final int COL_CATEGORY = 2;

  public static final int COL_APPROVED = 3;

  public static final int COL_DESCR = 4;

  public static final String[] CATEGORIES = {

    "Fares", "Logging", "Business meals", "Others"


  protected ExpenseReport m_parent;

  protected SimpleDateFormat m_frm;

  protected Vector m_vector;

  public ExpenseReportData(ExpenseReport parent) {

    m_parent = parent;

    m_frm = new SimpleDateFormat("MM/dd/yy");

    m_vector = new Vector();



  public void setDefaultData() {


    try {

      m_vector.addElement(new ExpenseData(

      m_frm.parse("04/06/99"), 200, 0, true,

        "Airline tickets"));

      m_vector.addElement(new ExpenseData(

        m_frm.parse("04/06/99"), 50,  2, false,

        "Lunch with client"));

      m_vector.addElement(new ExpenseData(

        m_frm.parse("04/06/99"), 120, 1, true,



    catch (java.text.ParseException ex) {}


  public int getRowCount() {

    return m_vector==null ? 0 : m_vector.size();


  public int getColumnCount() {

    return m_columns.length;


  public String getColumnName(int column) {

    return m_columns[column].m_title;


  public boolean isCellEditable(int nRow, int nCol) {

    return true;


  public Object getValueAt(int nRow, int nCol) {

    if (nRow < 0 || nRow>=getRowCount())

      return "";

    ExpenseData row = (ExpenseData)m_vector.elementAt(nRow);

    switch (nCol) {

      case COL_DATE: return m_frm.format(row.m_date);

      case COL_AMOUNT: return row.m_amount;

      case COL_CATEGORY: return CATEGORIES[row.m_category.intValue()];

      case COL_APPROVED: return row.m_approved;

      case COL_DESCR: return row.m_description;


    return "";


  public void setValueAt(Object value, int nRow, int nCol) {

    if (nRow < 0 || nRow>=getRowCount())


    ExpenseData row = (ExpenseData)m_vector.elementAt(nRow);

    String svalue = value.toString();

    switch (nCol) {

      case COL_DATE:

        Date  date = null;

        try {

          date = m_frm.parse(svalue);


        catch (java.text.ParseException ex) {

          date = null;


        if (date == null) {


            svalue+" is not a valid date",

            "Warning", JOptionPane.WARNING_MESSAGE);



        row.m_date = date;


      case COL_AMOUNT:

        try {

          row.m_amount = new Double(svalue);


        catch (NumberFormatException e) { break; }



      case COL_CATEGORY:

        for (int k=0; k<CATEGORIES.length; k++)

          if (svalue.equals(CATEGORIES[k])) {

            row.m_category = new Integer(k);




      case COL_APPROVED:

        row.m_approved = (Boolean)value;


      case COL_DESCR:

        row.m_description = svalue;




  public void insert(int row) {

    if (row < 0)

      row = 0;

    if (row > m_vector.size())

      row = m_vector.size();

    m_vector.insertElementAt(new ExpenseData(), row);


  public boolean delete(int row) {

    if (row < 0 || row >= m_vector.size())

      return false;


      return true;



Understanding the Code

Class ExpenseReport

Class ExpenseReport extends JFrame and defines three instance variables:

JTable m_table: table to edit data.

ExpenseReportData m_data: data model for this table.

JLabel m_total: label to dynamically display total amount of expenses.

The ExpenseReport constructor first instantiates our table model, m_data, and then instantiates our table, m_table. The selection mode is set to single selection and we iterate through the number of columns creating cell renderers and editors based on each specific column. The "Approved" column uses an instance of our custom CheckCellRenderer class as renderer. All other columns use a DefaultTableCellRenderer. All columns also use a DefaultCellEditor. However, the component used for editing varies: the "Category" column uses a JComboBox, the "Approved" column uses a JCheckBox, and all other columns use a JTextField. These components are passed to the DefaultTableCellRenderer constructor.

Several components are added to the bottom of our frame: JLabel m_total, used to display the total amount of expenses, and three JButtons used to manipulate tables rows. (Note that the horizontal glue component added between the label and the button pushes buttons to the right side of the panel, so they remain glued to the right when our frame is resized.)

These three buttons, titled "Insert before," "Insert after," and "Delete row," behave as their titles imply. The first two use the insert() method from the ExpenseReportData model to insert a new row before or after the currently selected row. The last one deletes the currently selected row by calling the delete() method. In all cases the modified table is updated and repainted.

Method calcTotal() calculates the total amount of expenses in column COL_AMOUNT using our table's data model, m_data.

Class CheckCellRenderer

Since we use check boxes to edit our table's "Approved" column, to be consistent we also need to use check boxes for that column's cell renderer (recall that cell renderers just act as "rubber stamps" and are not at all interactive). The only GUI component which can be used in the existing DefaultTableCellRenderer is JLabel, so we have to provide our own implementation of the TableCellRenderer interface. This class, CheckCellRenderer, uses JCheckBox as a super-class. Its constructor sets the border to indicate whether the component has the focus and sets its opaque property to true to indicate that the component's background will be filled with the background color.

The only method which must be implemented in the TableCellRenderer interface is getTableCellRendererComponent(). This method will be called each time the cell is about to be rendered to deliver new data to the renderer. It takes six parameters:

JTable table: reference to table instance.

Object value: data object to be sent to the renderer.

boolean isSelected: true if the cell is currently selected.

boolean hasFocus: true if the cell currently has the focus.

int row: cell's row.

int column: cell's column.

Our implementation sets whether the JCheckBox is checked depending on the value passed as Boolean. Then it sets the background, foreground, font, and border to ensure that each cell in the table has a similar appearance.

Class ExpenseData

Class ExpenseData represents a single row in the table. It holds five variables corresponding to our data structure described in the beginning of this section.

Class ColumnData

Class ColumnData holds each column's title, width, and header alignment.

Class ExpenseReportData

ExpenseReportData extends AbstractTableModel and should look somewhat familiar from previous examples in this chapter (e.g. StockTableData), so we will not discuss this class in complete detail. However, we need to take a closer look at the setValueAt() method, which is new for this example (all previous examples did not accept new data). This method is called each time an edit is made to a table cell. First we determine which ExpenseData instance (table's row) is affected, and if it is invalid we simply return. Otherwise, depending on the column of the changed cell, we define several cases in a switch structure to accept and store a new value, or to reject it:

For the "Date" column the input string is parsed using our SimpleDateFormat instance. If parsing is successful, a new date is saved as a Date object, otherwise an error message is displayed.

For the "Amount" column the input string is parsed as a Double and stored in the table if parsing is successful. Also a new total amount is recalculated and displayed in the "Total" JLabel.

For the "Category" column the input string is placed in the CATEGORIES array at the corresponding index and is stored in the table model.

For the "Approved" column the input object is cast to a Boolean and stored in the table model.

For the "Description" column the input string is directly saved in our table model.

Running the Code

Try editing different columns and note how the corresponding cell editors work. Experiment with adding and removing table rows and note how the total amount is updated each time the "Amount" column is updated. Figure 18.8 shows ExpenseReport with a combo box opened to change a cell's value.

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