Errors when appending to JTextArea
When I run my applet using the following code, I get all kinds of errors in the compiler (listed after the code). I'm not able to determine what is causing the errors, please help.....
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.table.*;
import java.text.DecimalFormat;
publicclass MtgCalculatorextends JFrameimplements ActionListener
{
//declarations for GUI
privatestaticdouble mortAmt=0.0;//double variable for loan amount
privatestaticdouble monthlyPay=0.0;//double variable for monthly payment
privatestaticdouble InterestRate=0.0;//double variable for interest rate
privatestaticint termLength=0;//integer variable for duration (term)
privateboolean clearText=true;//clear text flag for clearing text fields
privateint PaymentNumber=0;
privatedouble presMonthInt = 0.0;
privatedouble principlePaid = 0.0;
privatedouble monthEndPrinciple = 0.0;
DecimalFormat moneyFormat=new DecimalFormat("$###,###.00");//format pattern for currency values
DecimalFormat intRateFormat=new DecimalFormat("##.###%");//format pattern for Interest Rate (add % symbol)
DecimalFormat yearsFormat=new DecimalFormat("## years");//format pattern for duration (term)
JComboBox termRateText =new JComboBox(new String[]{"","7 years @ 5.35%","15 years @ 5.5%","30 years @ 5.75%"});
JTextField principleValueText =new JTextField();
JTextField pmtText =new JTextField(10);
JTextArea displayAmortInfo;
AbstractButton calcButton =new JButton(" Calculate ");
AbstractButton clrButton =new JButton("Clear Fields");
publicvoid buildGUI()
{
JFrame frame =new JFrame();
frame.setTitle("Mortgage Payment Calculator Version 5.0");
frame.getContentPane().add(getTopPanel(),BorderLayout.NORTH);
frame.getContentPane().add(getBottomPanel(),BorderLayout.CENTER);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setResizable(false);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
private JPanel getTopPanel()
{
JPanel panel =new JPanel(new BorderLayout());
JPanel topRow =new JPanel(new GridLayout(1,6));
topRow.add(new JLabel("Principle Value: ",JLabel.RIGHT));
topRow.add(principleValueText);
topRow.add(new JLabel("Loan Terms: ",JLabel.RIGHT));
topRow.add(termRateText);
JPanel bottomRow =new JPanel(new GridLayout(1,2));
JPanel leftSide =new JPanel();
leftSide.add(calcButton);
leftSide.add(clrButton);
JPanel rightSide =new JPanel();
rightSide.add(new JLabel("Monthly Payment: ",JLabel.RIGHT));
rightSide.add(pmtText);
bottomRow.add(leftSide);
bottomRow.add(rightSide);
calcButton.addActionListener(this);
clrButton.addActionListener(this);
panel.add(topRow,BorderLayout.NORTH);
panel.add(bottomRow,BorderLayout.SOUTH);
return panel;
}
private JPanel getBottomPanel()
{
JPanel panel =new JPanel(new BorderLayout());
JPanel topRow =new JPanel(new GridLayout(1,1));
topRow.add(new JLabel("Payment #", JLabel.LEFT));
topRow.add(new JLabel("Loan Balance", JLabel.LEFT));
topRow.add(new JLabel("Interest Paid", JLabel.LEFT));
JPanel bottomRow =new JPanel(new GridLayout(1,1));
JTextArea displayAmortInfo =new JTextArea(25, 50);
JScrollPane sp =new JScrollPane(displayAmortInfo);
panel.add(sp);
panel.add(topRow,BorderLayout.NORTH);
panel.add(bottomRow,BorderLayout.SOUTH);
return panel;
}
publicvoid actionPerformed(ActionEvent event)//activating the action event so the user's input is taken
{
//checking for user button clicks
if(event.getSource() == calcButton)//user clicks the Calculate button
{
clearText=false;//set clear text flag to false
int menuNum = termRateText.getSelectedIndex();
switch(menuNum){
case 0:
InterestRate=0.0;
termLength=0;
break;
case 1:
InterestRate=5.35;
termLength=7;
break;
case 2:
InterestRate=5.50;
termLength=15;
break;
case 3:
InterestRate=5.75;
termLength=30;
break;
}
mortAmt=new Double(principleValueText.getText().trim()).doubleValue();//parse LoanAmt to double
//calculate Monthly Payment amount for mortgage and display in Monthly Payment field
monthlyPay=(mortAmt*(InterestRate/(12*100)))/(1-Math.pow(1+(InterestRate/(12*100)),-(termLength*12)));//calculate
principleValueText.setText(moneyFormat.format(mortAmt));//set format for loan amount field
pmtText.setText(moneyFormat.format(monthlyPay));
while(PaymentNumber < termLength*12)//Starts the loop for displaying the table, loop
{//continues until all payments have been displayed
PaymentNumber++;
presMonthInt = mortAmt * (InterestRate/12);//this calculates the monthly interest paid
principlePaid = monthlyPay - presMonthInt;//this calculates the monthly principle paid
monthEndPrinciple = mortAmt - principlePaid;//this calculates what the principle after the payment
//Display the total loan information in text scroll area
displayAmortInfo.append(PaymentNumber +"\t"
+ moneyFormat.format(monthEndPrinciple) +"\t\t"
+ moneyFormat.format(presMonthInt)+"\n");
displayAmortInfo.setCaretPosition(0);
}//end while loop for Amortization table
}//end if for Calc button
elseif(event.getSource() == clrButton)//user clicks the Reset button
{
clearText=true;//set clear text flag to true for new calculation
principleValueText.setText("");//clears the mortgage amount field
pmtText.setText("");//clears the mortgage payment field
termRateText.setSelectedIndex(0);//clears the interest rate field
displayAmortInfo.setText("");
principleValueText.requestFocus();//return cursor to mortgage amount field
}//end else if for Reset button
}//end check for button clicks
publicstaticvoid main(String[] args)
{
SwingUtilities.invokeLater(new Runnable(){
publicvoid run(){
new MtgCalculator().buildGUI();}});
}
}
Here's the errors I'm getting:
java.lang.NullPointerException
at MtgCalculator.actionPerformed(MtgCalculator.java:132)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1786)
at javax.swing.AbstractButton$ForwardActionEvents.actionPerformed(AbstractButton.java:1839)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:420)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:258)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:245)
at java.awt.Component.processMouseEvent(Component.java:5100)
at java.awt.Component.processEvent(Component.java:4897)
at java.awt.Container.processEvent(Container.java:1569)
at java.awt.Component.dispatchEventImpl(Component.java:3615)
at java.awt.Container.dispatchEventImpl(Container.java:1627)
at java.awt.Component.dispatchEvent(Component.java:3477)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:3483)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3198)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3128)
at java.awt.Container.dispatchEventImpl(Container.java:1613)
at java.awt.Window.dispatchEventImpl(Window.java:1606)
at java.awt.Component.dispatchEvent(Component.java:3477)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:480)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:145)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:137)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:100)
