Not able to filter rows of jtable with textfield in netbeans

DBOperations objDB;
ArrayList alstStock;
public TableRowSorter sorter;
public void viewDailyStock() {
initComponents();
setSize(Toolkit.getDefaultToolkit().getScreenSize());
objDB = new DBOperations();
alstStock = objDB.getStockList();
generateTable();
txtSearch.getDocument().addDocumentListener(
        new DocumentListener() {
    @Override
            public void changedUpdate(DocumentEvent e) {
                newFilter();
            }
    @Override
            public void insertUpdate(DocumentEvent e) {
                newFilter();
            }
    @Override
            public void removeUpdate(DocumentEvent e) {
                newFilter();
            }
        });
setVisible(true);
}
void generateTable() {
Object data[][] = new Object[alstStock.size()][10];
String date = null;
for (int i = 0; i < alstStock.size(); i++) {
    StockBean objBean = (StockBean) alstStock.get(i);
    data[i][0] = i + 1;
    data[i][1] = objBean.getBrand();
    data[i][2] = objBean.getProductCode();
    data[i][3] = objBean.getProductName();
    data[i][8] = objBean.getItemInBox();
    SimpleDateFormat df = new SimpleDateFormat("EEEE, MMM d,yyyy");
    date = df.format(objBean.getDate());
    data[i][4] = date;
    data[i][5] = objBean.getUser();
    data[i][6] = objBean.getLotNumber();
    data[i][7] = objBean.getQtyInItem();
    data[i][9] = objBean.getQtyInBox();
}
String header[] = {"S.No.", "Brand", "Code", "Name", "Date", "Added By", "Lot No.", "Qty In Item", "Item", "Qty In Boxes"};

tblStock = new JTable(data,header);
sorter=new TableRowSorter(tblStock.getModel());
tblStock.setRowSorter(sorter);
jScrollPane1.setViewportView(tblStock);
setWidth();
tblStock.setAutoCreateRowSorter(true);

}
public void newFilter() {
RowFilter rf = null;
try {
    rf = RowFilter.regexFilter(txtSearch.getText(), 3);
} catch (java.util.regex.PatternSyntaxException e) {
    System.out.println("Exception "+e);
}
sorter.setRowFilter(rf);
}

DBOperations is a class for fetching data from database table. StockBean is a class of object with the getter and setter method.

This is my code of implementing row filter to the 4th column of jtable with a textfield but its not working means it is not filtering data and even i am not getting any exception. Please help me...