Rebuild table when actionperformed

Question

I'm trying to rebuild my table to reflect the changed data when my calculate button is clicked. I'm getting a null pointer exception on compile
public class DennisBillingsWK3 extends JPanel implements ActionListener
     private double principal = 200000; 
     private int term[] = {30, 15, 7};               
     private double interestRate[] = {5.75, 5.5, 5.35};
     private double payment = calcPayment(0); 
     private String data[] = {"30 years at 5.75%", "15 years at 5.5%", "7 years at 5.35%"};
     private Object tableData[][];
     String[] colNames = {"Period", "Payment", "Interest", "Loan Balance"};
     private JLabel jlPrincipal;
     private JLabel jlLoanOptions;
     private JLabel jlPayment;
     private JScrollPane scrollPane;
     private JButton calculate;
     private JButton exit;
     private JFormattedTextField ftfPrincipal;
     private JFormattedTextField ftfPayment;
     private JTable table;
     private JComboBox loanOptions;
     public static void main(String[] args)
          DennisBillingsWK3 loan = new DennisBillingsWK3();
          loan.createGUI();
     public DennisBillingsWK3()
          super(new BorderLayout());
          jlPrincipal = new JLabel("Principal: ");
          jlPayment = new JLabel("Payment: ");
          jlLoanOptions = new JLabel("Loan options");
          ftfPrincipal = new JFormattedTextField();
          ftfPrincipal.setValue(new Double(principal));
          ftfPrincipal.setColumns(10);
          ftfPrincipal.addActionListener(this);
          ftfPayment = new JFormattedTextField();
          ftfPayment.setValue(new Double(payment));
          ftfPayment.setColumns(10);
          ftfPayment.setEditable(false);
          ftfPayment.setForeground(Color.black);
          table = new JTable();
          JScrollPane scrollPane = new JScrollPane(table);
          table.setFillsViewportHeight(true);
          loanOptions = new JComboBox(data);
          jlPrincipal.setLabelFor(ftfPrincipal);
          jlPayment.setLabelFor(ftfPayment);
          jlLoanOptions.setLabelFor(loanOptions);
          JPanel labelPane = new JPanel(new GridLayout(0,1));
          labelPane.add(jlPrincipal);
          labelPane.add(jlLoanOptions);
          labelPane.add(jlPayment);
          JPanel fieldPane = new JPanel(new GridLayout(0,1));
          fieldPane.add(ftfPrincipal);
          fieldPane.add(loanOptions);
          fieldPane.add(ftfPayment);
          JButton calculate = new JButton("Calculate");
          calculate.setActionCommand("calculate");
          calculate.addActionListener(this);
          JButton exit = new JButton("Exit");
          exit.setActionCommand("exit");
          exit.addActionListener(this);
          JButton clear = new JButton("Clear");
          clear.setActionCommand("clear");
          clear.addActionListener(this);
          JPanel buttonPane = new JPanel(new GridLayout(0,1));
          buttonPane.add(calculate);
          buttonPane.add(exit);
          buttonPane.add(clear);
          setBorder (BorderFactory.createEmptyBorder(30, 30, 30, 30));
          add(labelPane, BorderLayout.CENTER);
          add(fieldPane, BorderLayout.EAST);
          add(buttonPane, BorderLayout.SOUTH);
          add(scrollPane, BorderLayout.NORTH);
     public void createGUI()
          JFrame frame = new JFrame("Mortgage Calculator");
          frame.setBounds(350,300,600,150);
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frame.add(new DennisBillingsWK3());
          frame.pack();
          frame.setVisible(true);
     public double calcPayment(int i)
          double adjRate = interestRate/(12*100);
          int adjTerm = term[i]*12;
          payment=principal*((adjRate*Math.pow((1+adjRate),adjTerm))/(Math.pow((1+adjRate),adjTerm)-1));
          BigDecimal hundredths = new BigDecimal(payment);
          hundredths = hundredths.setScale(2, BigDecimal.ROUND_UP);
          return hundredths.doubleValue();
     public void calcAmortTable(int i)
          double adjRate = interestRate[i]/(12*100);
          int adjTerm = term[i]*12;
          payment = calcPayment(i);
          double interest;
          double runningPrincipal = principal;
          DecimalFormat money = new DecimalFormat("$0.00");
          tableData = new Object[adjTerm][4];
          for(int x=0; x<adjTerm; x++) {
               interest = adjRate*runningPrincipal;
               runningPrincipal -= payment - interest;
               tableData[x][0]= x+1;
               tableData[x][1]= money.format(payment);
               tableData[x][2]= money.format(interest);
               tableData[x][3]= money.format(runningPrincipal);
          table = new JTable(tableData, colNames);
          scrollPane.add(table);
          scrollPane.validate();
     public void actionPerformed(ActionEvent e)
          if("calculate".equals(e.getActionCommand())) {
               try {
                         if(principal <= 0 || ftfPrincipal.getValue() == null) {
                              throw new NumberFormatException();
                         principal = ((Number)ftfPrincipal.getValue()).doubleValue();
                         int loanIndex = loanOptions.getSelectedIndex();
                         ftfPrincipal.setValue(principal);
                         ftfPayment.setValue(calcPayment(loanIndex));
                         calcAmortTable(loanIndex);
               catch(NumberFormatException err)
                         JOptionPane.showMessageDialog(null,"No fields can be 0 or empty","Error",JOptionPane.INFORMATION_MESSAGE);
          if("exit".equals(e.getActionCommand())) {
               System.exit(0);//System.exit closes application     
          if("clear".equals(e.getActionCommand())) {
               ftfPrincipal.setValue(null);
               ftfPayment.setValue(null);

Answer 1

I snipped the code out of my constructor and removed the field and I made the following changes but my table doesn't show. I don't get any error or exceptions but not table
Here's my constructor and calcAmortTable respectively
public DennisBillingsWK3()
          // The super keyword calls the constructor from the parent class JPanel
          super(new BorderLayout());
          //set values for textfield labels
          jlPrincipal = new JLabel("Principal: ");
          jlPayment = new JLabel("Payment: ");
          jlLoanOptions = new JLabel("Loan options");
          //Setup text fields, initial value, number of positions and action listener
          ftfPrincipal = new JFormattedTextField();
          ftfPrincipal.setValue(new Double(principal));
          ftfPrincipal.setColumns(10);
          ftfPrincipal.addActionListener(this);
          ftfPayment = new JFormattedTextField();
          ftfPayment.setValue(new Double(payment));
          ftfPayment.setColumns(10);
          ftfPayment.setEditable(false);
          ftfPayment.setForeground(Color.black);
          //Setup amortization table
          table = new JTable();
          table.setFillsViewportHeight(true);
          //Setup combo box
          loanOptions = new JComboBox(data);
          //Attach labels to text fields
          jlPrincipal.setLabelFor(ftfPrincipal);
          jlPayment.setLabelFor(ftfPayment);
          jlLoanOptions.setLabelFor(loanOptions);
          //set labels and fields in a grid
          JPanel labelPane = new JPanel(new GridLayout(0,1));
          labelPane.add(jlPrincipal);
          labelPane.add(jlLoanOptions);
          labelPane.add(jlPayment);
          //create panel for textfields and add fields
          JPanel fieldPane = new JPanel(new GridLayout(0,1));
          fieldPane.add(ftfPrincipal);
          fieldPane.add(loanOptions);
          fieldPane.add(ftfPayment);
          //create buttons, set action commands and listener to be used in ActionPerformed method
          JButton calculate = new JButton("Calculate");
          calculate.setActionCommand("calculate");
          calculate.addActionListener(this);
          JButton exit = new JButton("Exit");
          exit.setActionCommand("exit");
          exit.addActionListener(this);
          JButton clear = new JButton("Clear");
          clear.setActionCommand("clear");
          clear.addActionListener(this);
          //Create panel for buttons
          JPanel buttonPane = new JPanel(new GridLayout(0,1));
          buttonPane.add(calculate);
          buttonPane.add(exit);
          buttonPane.add(clear);
          //set border for GUI and add panels to container
          setBorder (BorderFactory.createEmptyBorder(30, 30, 30, 30));
          add(labelPane, BorderLayout.CENTER);
          add(fieldPane, BorderLayout.EAST);
          add(buttonPane, BorderLayout.SOUTH);
public void calcAmortTable(int i)
          double adjRate = interestRate/(12*100);
          int adjTerm = term[i]*12;
          payment = calcPayment(i);
          double interest;
          double runningPrincipal = principal;
          DecimalFormat money = new DecimalFormat("$0.00");
          tableData = new Object[adjTerm][4];
          for(int x=0; x<adjTerm; x++) {
               interest = adjRate*runningPrincipal;
               runningPrincipal -= payment - interest;
               tableData[x][0]= x+1;
               tableData[x][1]= money.format(payment);
               tableData[x][2]= money.format(interest);
               tableData[x][3]= money.format(runningPrincipal);
          table = new JTable(tableData, colNames);
          JScrollPane scrollPane = new JScrollPane();
          table.setFillsViewportHeight(true);
          add(scrollPane, BorderLayout.NORTH);