How to add and subtract value of sum after adding/removing a row from JTable

I have the code for adding and removing a single row for my JTable but it causes problems like not providing accurate calculation of overall sum and subtraction after removing it from the JTable. The JTable serves as a "cart" for adding and removing items in the cart.

The add to cart button for adding a row to the cart:

if (e.getSource() == movebutton) {
        TableModel model1 = productTable.getModel();
        int index[] = productTable.getSelectedRows();
        Object[] row = new Object[4];
        DefaultTableModel model2 = (DefaultTableModel) cartTable.getModel();

        for (int i = 0; i < index.length; i++) {
            row[0] = model1.getValueAt(index[i], 0);
            row[1] = model1.getValueAt(index[i], 1);
            row[2] = model1.getValueAt(index[i], 2);
            model2.addRow(row);
            getSum();
        }

The code where it adds the overall items:

public void getSum() {  //column 02 is where the item's prices are listed
    for (int i = 0; i < cartTable.getRowCount(); i++) {
        total += Double.parseDouble(cartTable.getValueAt(i, 2).toString()); 
    }
    cartAmount.setText("Total: P " + Double.toString(total));
}

}

The remove an item from the cart button code:

 try {
            for (int i = 0; i < cartTable.getRowCount(); i++) {
                total = total - Double.parseDouble(cartTable.getValueAt(i, 2).toString());
            }
            cartAmount.setText("Total: P " + Double.toString(total));
            if (total <= 0.0) {
                total = 0.0;
            }
            {
                int getSelectedRowForDeletion = cartTable.getSelectedRow();
                model2.removeRow(getSelectedRowForDeletion);
                JOptionPane.showMessageDialog(null, "Item removed from cart");
            }
        } catch (NumberFormatException ex) {
            ex.printStackTrace();
        } catch (ArrayIndexOutOfBoundsException ex) {
        }
    }

Here are some pics when adding and remove an item:

How can I also make the remove button to not work when no row is selected? Like ask the user to select a row before deletion? Also remove the possibility of having negative sum calculations. Thank you

I solved it:

The add to cart button:

 if (e.getSource() == movebutton) {
        try {
            int index[] = productTable.getSelectedRows();
            Object[] row = new Object[4];

            for (int i = 0; i < index.length; i++) {
                row[0] = model.getValueAt(index[i], 0);
                row[1] = model.getValueAt(index[i], 1);
                row[2] = model.getValueAt(index[i], 2);
                model2.addRow(row);
            }
            DefaultTableModel t = (DefaultTableModel) productTable.getModel();
            int selectedRow = productTable.getSelectedRow();
                {
                    total += Double.parseDouble(t.getValueAt(selectedRow, 2).toString());
                }
                cartAmount.setText("Total: P " + Double.toString(total));
            }catch (ArrayIndexOutOfBoundsException a) {
        }
    }

The remove button:

if (e.getSource() == remove) {
        try {
            DefaultTableModel t = (DefaultTableModel) cartTable.getModel();
            int getSelectedRowForDeletion = cartTable.getSelectedRow();
            if (getSelectedRowForDeletion >= 0) {
                int selectedRow = cartTable.getSelectedRow();
                total -= Double.parseDouble(t.getValueAt(selectedRow, 2).toString());
                cartAmount.setText("Total: P " + Double.toString(total));
                model2.removeRow(getSelectedRowForDeletion);
                JOptionPane.showMessageDialog(null, "Item removed from cart!");
            } else {
                JOptionPane.showMessageDialog(null, "Select an item to remove.");
            }
        } catch (ArrayIndexOutOfBoundsException a) {
        }
    }

I removed the for loop when adding the values as it will just add the next item in the productTable. Same goes for the remove button.