Problem in event handling of combo box in JTable cell

Question

Hi,
I have a combo box as an editor for a column cells in JTable. I have a event listener for this combo box. When ever I click on the JTable cell whose editor is combo box,
I get the following exception,
Exception occurred during event dispatching:
java.lang.NullPointerException
     at javax.swing.plaf.basic.BasicTableUI$MouseInputHandler.setDispatchComponent(Unknown Source)
     at javax.swing.plaf.basic.BasicTableUI$MouseInputHandler.mousePressed(Unknown Source)
     at java.awt.AWTEventMulticaster.mousePressed(Unknown Source)
     at java.awt.Component.processMouseEvent(Unknown Source)
     at java.awt.Component.processEvent(Unknown Source)
     at java.awt.Container.processEvent(Unknown Source)
     at java.awt.Component.dispatchEventImpl(Unknown Source)
     at java.awt.Container.dispatchEventImpl(Unknown Source)
     at java.awt.Component.dispatchEvent(Unknown Source)
     at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
     at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
     at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
     at java.awt.Container.dispatchEventImpl(Unknown Source)
     at java.awt.Component.dispatchEvent(Unknown Source)
     at java.awt.EventQueue.dispatchEvent(Unknown Source)
     at java.awt.EventDispatchThread.pumpOneEventForHierarchy(Unknown Source)
     at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
     at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
     at java.awt.EventDispatchThread.run(Unknown Source)
Can any one tell me how to over come this problem.
Thanks,
Raghu

Answer 1

Here's an example of the model I used in my JTable. I've placed 2 comboBoxes with no problems.
Hope this helps.
public class FileModel5 extends AbstractTableModel
public boolean isEditable = false;
protected static int NUM_COLUMNS = 3;
// initialize number of rows to start out with ...
protected static int START_NUM_ROWS = 0;
protected int nextEmptyRow = 0;
protected int numRows = 0;
static final public String file = "File";
static final public String mailName = "Mail Id";
static final public String postName = "Post Office Id";
static final public String columnNames[] = {"File", "Mail Id", "Post Office Id"};
// List of data
protected Vector data = null;
public FileModel5()
data = new Vector();
public boolean isCellEditable(int rowIndex, int columnIndex)
// The 2nd & 3rd column or Value field is editable
if(isEditable)
if(columnIndex > 0)
return true;
return false;
* JTable uses this method to determine the default renderer/
* editor for each cell. If we didn't implement this method,
* then the last column would contain text ("true"/"false"),
* rather than a check box.
public Class getColumnClass(int c)
return getValueAt(0, c).getClass();
* Retrieves number of columns
public synchronized int getColumnCount()
return NUM_COLUMNS;
* Get a column name
public String getColumnName(int col)
return columnNames[col];
* Retrieves number of records
public synchronized int getRowCount()
if (numRows < START_NUM_ROWS)
return START_NUM_ROWS;
else
return numRows;
* Returns cell information of a record at location row,column
public synchronized Object getValueAt(int row, int column)
try
FileRecord5 p = (FileRecord5)data.elementAt(row);
switch (column)
case 0:
return (String)p.file;
case 1:
return (String)p.mailName;
case 2:
return (String)p.postName;
catch (Exception e)
return "";
public void setValueAt(Object aValue, int row, int column)
FileRecord5 arow = (FileRecord5)data.elementAt(row);
arow.setElementAt((String)aValue, column);
fireTableCellUpdated(row, column);
* Returns information of an entire record at location row
public synchronized FileRecord5 getRecordAt(int row) throws Exception
try
return (FileRecord5)data.elementAt(row);
catch (Exception e)
throw new Exception("Record not found");
* Used to add or update a record
* @param tableRecord
public synchronized void updateRecord(FileRecord5 tableRecord)
String file = tableRecord.file;
FileRecord5 p = null;
int index = -1;
boolean found = false;
boolean addedRow = false;
int i = 0;
while (!found && (i < nextEmptyRow))
p = (FileRecord5)data.elementAt(i);
if (p.file.equals(file))
found = true;
index = i;
} else
i++;
if (found)
{ //update
data.setElementAt(tableRecord, index);
else
if (numRows <= nextEmptyRow)
//add a row
numRows++;
addedRow = true;
index = nextEmptyRow;
data.addElement(tableRecord);
//Notify listeners that the data changed.
if (addedRow)
nextEmptyRow++;
fireTableRowsInserted(index, index);
else
fireTableRowsUpdated(index, index);
* Used to delete a record
public synchronized void deleteRecord(String file)
FileRecord5 p = null;
int index = -1;
boolean found = false;
int i = 0;
while (!found && (i < nextEmptyRow))
p = (FileRecord5)data.elementAt(i);
if (p.file.equals(file))
found = true;
index = i;
} else
i++;
if (found)
data.removeElementAt(i);
nextEmptyRow--;
numRows--;
fireTableRowsDeleted(START_NUM_ROWS, numRows);
* Clears all records
public synchronized void clear()
int oldNumRows = numRows;
numRows = START_NUM_ROWS;
data.removeAllElements();
nextEmptyRow = 0;
if (oldNumRows > START_NUM_ROWS)
fireTableRowsDeleted(START_NUM_ROWS, oldNumRows - 1);
fireTableRowsUpdated(0, START_NUM_ROWS - 1);
* Loads the values into the combo box within the table for mail id
public void setUpMailColumn(JTable mapTable, ArrayList mailList)
TableColumn col = mapTable.getColumnModel().getColumn(1);
javax.swing.JComboBox comboMail = new javax.swing.JComboBox();
int s = mailList.size();
for(int i=0; i<s; i++)
comboMail.addItem(mailList.get(i));
col.setCellEditor(new DefaultCellEditor(comboMail));
//Set up tool tips.
DefaultTableCellRenderer renderer = new DefaultTableCellRenderer();
renderer.setToolTipText("Click for mail Id list");
col.setCellRenderer(renderer);
//Set up tool tip for the mailName column header.
TableCellRenderer headerRenderer = col.getHeaderRenderer();
if (headerRenderer instanceof DefaultTableCellRenderer)
((DefaultTableCellRenderer)headerRenderer).setToolTipText(
"Click the Mail Id to see a list of choices");
* Loads the values into the combo box within the table for post office id
public void setUpPostColumn(JTable mapTable, ArrayList postList)
TableColumn col = mapTable.getColumnModel().getColumn(2);
javax.swing.JComboBox combo = new javax.swing.JComboBox();
int s = postList.size();
for(int i=0; i<s; i++)
combo.addItem(postList.get(i));
col.setCellEditor(new DefaultCellEditor(combo));
//Set up tool tips.
DefaultTableCellRenderer renderer = new DefaultTableCellRenderer();
renderer.setToolTipText("Click for post office Id list");
col.setCellRenderer(renderer);
//Set up tool tip for the mailName column header.
TableCellRenderer headerRenderer = col.getHeaderRenderer();
if (headerRenderer instanceof DefaultTableCellRenderer)
((DefaultTableCellRenderer)headerRenderer).setToolTipText(
"Click the Post Office Id to see a list of choices");
}