private void initializeTable() {
        ImageIcon plusIcon = new ImageIcon(getClass().getResource("/images/btnPlus.png"));
        ImageIcon minusIcon = new ImageIcon(getClass().getResource("/images/btnMinus.png"));
        plusIcon = new ImageIcon(plusIcon.getImage().getScaledInstance(28, 28, java.awt.Image.SCALE_SMOOTH));
        minusIcon = new ImageIcon(minusIcon.getImage().getScaledInstance(28, 28, java.awt.Image.SCALE_SMOOTH));
        btnNextYear.setIcon(plusIcon);
        btnPreviousYear.setIcon(minusIcon);
        btnNextMonth.setIcon(plusIcon);
        btnPreviousMonth.setIcon(minusIcon);
        tblTimesheet.setModel(new DefaultTableModel() {
            @Override
            public boolean isCellEditable(int rowIndex, int colIndex) {
                return !model.getColumnName(colIndex).contains("Compensatie") && colIndex != 0 && !model.getColumnName(colIndex).equals("Ingeroosterd") && !model.getColumnName(colIndex).equals("Totaal") && !model.getValueAt(rowIndex, 0).toString().equals("Totaal");
            }

            @Override
            public void fireTableCellUpdated(int row, int column) {
                if (column < model.getColumnCount() - 4 && !model.getValueAt(row, 0).equals("Totaal")) {
                    calculateTotal();
                }
                super.fireTableCellUpdated(row, column);
            }
        });
    }