NullPointerException on creating JTable

Question

I have written my own TableModel to be able to get a CheckBox as the CellEditor for Boolean object as stated in the Java tutorial.
When I try to create the TableModel I get a NullPointerException in the method getRowCount. However, I have checked, and have determined that getRowCount() gets called BEFORE the constructor, thus the data is not initialized, and the NullPointerException follows.
Anyone can help?
D
package b2bwft.interfaces.graphical.workflow;
import javax.swing.table.*;
import java.util.Vector;
import java.util.Iterator;
public class InputTableModel extends DefaultTableModel
  public static boolean DEBUG = true;
  final String[] columnNames = {"Manual Input"};
  Vector dataVect = null;
  Object[][] data = null;
  public InputTableModel()
  public InputTableModel(Vector types)
    data = new Object[types.size()][1];
    for (int i=0;i<types.size();i++)
      data[0] = types.elementAt(i);
dataVect = types;
public int getColumnCount()
return columnNames.length;
public int getRowCount()
return dataVect.size();
public String getColumnName(int col)
return columnNames[col];
public Object getValueAt(int row, int col)
return data[row][col];
* 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();
* Don't need to implement this method unless your table's
* editable.
public boolean isCellEditable(int row, int col)
//Note that the data/cell address is constant,
//no matter where the cell appears onscreen.
return true;
* Don't need to implement this method unless your table's
* data can change.
public void setValueAt(Object value, int row, int col)
if (DEBUG)
System.out.println("Setting value at " + row + "," + col
+ " to " + value
+ " (an instance of "
+ value.getClass() + ")");
data[row][col] = value;
fireTableCellUpdated(row, col);
if (DEBUG)
System.out.println("New value of data:");
printDebugData();
private void printDebugData()
int numRows = getRowCount();
int numCols = getColumnCount();
for (int i=0; i < numRows; i++)
System.out.print(" row " + i + ":");
for (int j=0; j < numCols; j++)
System.out.print(" " + data[i][j]);
System.out.println();
System.out.println("--------------------------");

Answer 1

Two things to check:
1) Make sure the default constructor on the model is not being called - that would cause the NPE to be thrown.
2) Print out the objects in the types Vector in the constructor call to make sure it is populated.
As an aside, if you don't need synchronization, you should be using java.util.ArrayList rather than java.util.Vector - it's more efficient.