How do I create a JTable with some empty cells in it?

Question

I have a three column JTable. The first column is a String showing description. The second column contains numbers (double) and the third column also contains numbers. In some cases not all cells in a row should contain data. So for instance, I could have row one showing only description (a String in the first column), and then row two showing description (a String in the first column) and a number (a double in the second column) in columns one and two respectively. My problem is that, the data gets copied from the cells with data to the cells which are supposed to be empty. So, how do I create a JTable with some empty cells in it.

Answer 1

I have tried empty strings for those values, but it did not work. My table puts objects in an arraylist called reconciliation. The arraylist takes different objects with the same super class. The code below explains. Are you suggesting I pass null to my constructor?
JTable table = new JTable(new ReconTableModel());The method below is from the table model
protected  List<Reconciliation> reconciliation = new ArrayList<Reconciliation>();
protected void fillModel(){
      reconciliation.add(new CashBook("Cash Book Report"," "," "));
      reconciliation.add(new CheckingBankAccount("Checking Bank Account"," "," "));
      reconciliation.add(new BankBalance("Bank Balance As Per Bank Statement",500," "));
      reconciliation.add(new PaymentVouchers("Payment Voucher Receipt",300," "));
      reconciliation.add(new DepositVoucher("Deposit Voucher Receipt",1000," "));
      reconciliation.add(new ReconciledBalance("Reconcilied Bank Balance",1200," "));
      reconciliation.add(new BalanceAt("Bank Balance At",800," "));
      reconciliation.add(new Difference("Difference",400," "));
      Collections.sort( reconciliation, new Comparator<Reconciliation>(){
      public int compare( Reconciliation a, Reconciliation b) {
        return a.getTransactionName().compareTo( b.getTransactionName());
  }