public Class getColumnClass(int c) {
    return getValueAt(0, c).getClass();
}

public Class getColumnClass(int columnIndex) {
    Object obj = getValueAt(0, columnIndex);
    if (obj == null) return Object.class;
    return obj.getClass();
}

Successfully connected to the database: jdbc:postgresql://localhost:5433/sample_db
    Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at com.jdbc.ui.EmployeeTableModel.getValueAt(EmployeeTableModel.java:49)
    at com.jdbc.ui.EmployeeTableModel.getColumnClass(EmployeeTableModel.java:71)
    at javax.swing.JTable.getColumnClass(JTable.java:2698)
    at javax.swing.JTable.getCellRenderer(JTable.java:5674)
    at javax.swing.plaf.basic.BasicTableUI.paintCell(BasicTableUI.java:2113)
    at javax.swing.plaf.basic.BasicTableUI.paintCells(BasicTableUI.java:2016)
    at javax.swing.plaf.basic.BasicTableUI.paint(BasicTableUI.java:1812)
    at javax.swing.plaf.ComponentUI.update(ComponentUI.java:161)
    at javax.swing.JComponent.paintComponent(JComponent.java:780)
    at javax.swing.JComponent.paint(JComponent.java:1056)
    at javax.swing.JComponent.paintToOffscreen(JComponent.java:5210)

public class EmployeeTableModel extends AbstractTableModel {

private static final int EMPNO_COL = 0;
private static final int ENAME_COL = 1;
private static final int JOB_COL = 2;
private static final int MGR_COL = 3;
private static final int HIREDATE_COL = 4;
private static final int SAL_COL = 5;
private static final int COMM_COL = 6;
private static final int DEPTNO_COL = 7;

private String[] columnNames = { "empno", "ename", "job", "mgr", "hiredate", "sal", "comm", "deptno"};
private List<Employee> employees;

public EmployeeTableModel(List<Employee> theEmployees) {
    employees = theEmployees;
}

@Override
public int getColumnCount() {
    return columnNames.length;
}

@Override
public int getRowCount() {
    return employees.size();
}

@Override
public String getColumnName(int colNumber) {
    return columnNames[colNumber];
}

@Override
public Object getValueAt(int row, int col) {

    Employee tempEmployee = employees.get(row);

    switch (col) {
        case EMPNO_COL:
            return tempEmployee.getEmpno();
        case ENAME_COL:
            return tempEmployee.getEname();
        case JOB_COL:
            return tempEmployee.getJob();
        case MGR_COL:
            return tempEmployee.getMgr();
        case HIREDATE_COL:
            return tempEmployee.getHiredate();
        case SAL_COL:
            return tempEmployee.getSal();
        case COMM_COL:
            return tempEmployee.getComm();
        case DEPTNO_COL:
            return tempEmployee.getDeptno();
        default:
            return Object.class;
    }
}

@Override
public Class getColumnClass(int columnIndex) {
    Object obj = getValueAt(0, columnIndex);
    if (obj == null) return Object.class;
    return obj.getClass();
}
}

public class EmployeeApp extends JFrame {
private JPanel panelMain;
private JButton searchButton;
private JScrollPane scrollPane;
private JTextField idTextField;
private JLabel lastNameLabel;
private JTable table;

private EmployeesDao employeesDao;


public EmployeeApp() {

    // create the DAO
    try {
        employeesDao = new EmployeesDao();
    } catch (Exception exc) {
        JOptionPane.showMessageDialog(this, "Error: " + exc, "Error", JOptionPane.ERROR_MESSAGE);
    }

    searchButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            String searchValue = idTextField.getText();
            Employee singleEmployee;
            List<Employee> employees = null;

            try {

                int numValue = Integer.parseInt(searchValue);
                singleEmployee = employeesDao.getEmployeeById(numValue);
                employees = Collections.singletonList(singleEmployee);

                    // create the model and update the table
                    EmployeeTableModel empModel1 = new EmployeeTableModel(employees);
                    table.setModel(empModel1);


            } catch (NumberFormatException | SQLException | NullPointerException exc) {
                //JOptionPane.showMessageDialog(EmployeeApp.this, "Error: " + exc, "Error", JOptionPane.ERROR_MESSAGE);

                if (searchValue != null && searchValue.trim().length() > 0) {
                    try {
                        employees = employeesDao.searchEmployees(searchValue);
                    } catch (Exception e1) {
                        e1.printStackTrace();
                    }
                    // create the model and update the table
                    EmployeeTableModel empModel2 = new EmployeeTableModel(employees);
                    table.setModel(empModel2);
                } else {
                    try {
                        employees = employeesDao.getAllEmployees();
                    } catch (SQLException e1) {
                        e1.printStackTrace();
                    }
                    // create the model and update the table
                    EmployeeTableModel empModel3 = new EmployeeTableModel(employees);
                    table.setModel(empModel3);
                }

            }

        }

    });

    table = new JTable();
    scrollPane.setViewportView(table);
}


public static void main(String[] args) {
    JFrame frame = new JFrame("EmployeeApp");
    frame.setContentPane(new EmployeeApp().panelMain);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.pack();
    frame.setVisible(true);
}