Thread: I do not know how to fix this.

I am having a proble with my program. It compiles fine, but when I try to run, I ge tthe following:

Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Unknown Source)
at java.awt.Container.add(Unknown Source)
at MortCalcGUI.<init>(MtgCalc.java:293)
at MtgCalc.main(MtgCalc.java:13)

Here is the code:

import java.text.*;
import java.awt.event.*;
import javax.swing.*;
 
 
public class MtgCalc{
 
 
   public static void main (String[]args){
 
 
	      JFrame window = new MortCalcGUI();
		  window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		  window.setVisible(true);
	}
 
}

 class MortCalcGUI extends JFrame implements ActionListener{
 
      /*declare variables for GUI functions*/
        protected JButton bCal7,bCal15,bCal30, bClear, bExit;
		protected JLabel labelPayment, labelLoanAmount, labelTitle, labelInstructions, labelAmTable;
		protected JTextField fieldPayment, fieldLoanAmount;
		protected JTextArea areaAmTable;
		private static final long serialVersionUID = 1L;
 
 
		/*declare loan array data  and variables and initialize*/
		double intPaid, prinPaid,balance, mthlyPayment, loanAmount;
		int[]loanTerm = {7,15,30};
		double[] intRate = {5.35,5.50,5.75};
		double loanAmt = loanAmount;
 
		public void actionPerformed (ActionEvent e){
 
		  /*action taken depending on what button is selected*/
		  if ("Calculate7".equals(e.getActionCommand())){
 
 
 
				NumberFormat currency = NumberFormat.getCurrencyInstance();
 
				double paymentAmount = CalculatePayment7();
 
				fieldPayment.setText(""+ (currency.format(paymentAmount)));
 
				areaAmTable.append("Payment # \t Remaining Balance \t Interest Paid\n");	
 
		      /*set loan amount */
				loanAmt = Double.parseDouble(fieldLoanAmount.getText());
 
				for (int x = 1; x <= (loanTerm[0]*12); x++){
				/*this loops monthly payments for loans*/
 
				       balance=loanAmount;
						 /* sets Balance to the amount of the loan*/
 
						 /*monthly payment calculations*/
 
						 intPaid = (((intRate[0]/100.0)/12.0)*balance);
						 prinPaid = (paymentAmount -intPaid);
						 loanAmt =(balance-prinPaid);
 
						 areaAmTable.append(x + "\t" +currency.format(loanAmt) + " \t\t " + currency.format(intPaid) + "\n");
						 }
 
						 if (balance <= 0){ /*Until Balance is zero*/
 
						          areaAmTable.append ("\tRemaining balance =$0.00");
 
						}
 
			}	 
 
 
			else if ("Calculate15".equals(e.getActionCommand())){
 
 
				NumberFormat currency = NumberFormat.getCurrencyInstance();
 
				double paymentAmount = CalculatePayment15();
 
				fieldPayment.setText(""+ (currency.format(paymentAmount)));
 
				areaAmTable.append("Payment # \t Remaining Balance \t Interest Paid\n");	
 
		      /*set loan amount */
				loanAmt = Double.parseDouble(fieldLoanAmount.getText());
 
				for (int x = 1; x <= (loanTerm[1]*12); x++){
				/*this loops monthly payments for loans*/
 
				       balance=loanAmount;
						 /* sets Balance to the amount of the loan*/
 
						 /*montlhy payment calculations*/
 
						 intPaid = (((intRate[1]/100.0)/12.0)*balance);
						 prinPaid = (paymentAmount -intPaid);
						 loanAmt =(balance-prinPaid);
 
						 areaAmTable.append(x + "\t" +currency.format(loanAmt) + " \t\t " + currency.format(intPaid) + "\n");
						 }
 
						 if (balance <= 0){ /*Until Balance is zero*/
 
						          areaAmTable.append ("\tRemaining balance =$0.00");
 
						}
 
			}	 
 
 
 
         else if ("Calculate30".equals(e.getActionCommand())){
 
 
				    NumberFormat currency = NumberFormat.getCurrencyInstance();
 
				    double paymentAmount = CalculatePayment30();
 
				    fieldPayment.setText(""+ (currency.format(paymentAmount)));
 
				    areaAmTable.append("Payment # \t Remaining Balance \t Interest Paid\n");	
 
		          loanAmt = Double.parseDouble(fieldLoanAmount.getText());
 
 
					 for (int x = 1; x <= (loanTerm[2]*12); x++){
 
 
				           balance=loanAmount;
 
 
						     intPaid = (((intRate[2]/100.0)/12.0)*balance);
						     prinPaid = (paymentAmount -intPaid);
						     loanAmt =(balance-prinPaid);
 
						     areaAmTable.append(x + "\t" +currency.format(loanAmt) + " \t\t " + currency.format(intPaid) + "\n");
						 }
 
						 if (balance <= 0){ /*Until Balance is zero*/
 
						          areaAmTable.append ("\tRemaining balance =$0.00");
 
						}
 
			}	 
 
 
                 else if ("Clear".equals(e.getActionCommand())){
 
					          ClearFields ();
					  }
 
					  else {
 
					  System.exit (0);
 
					  }
 
		 }
 
 
		 public double CalculatePayment7 (){
 
		 /*checks input for incorrect input type*/
 
		    try {
		          /*If input is corect,then perform calculation*/
		          fieldPayment.setText ("");
				    double Payment = (loanAmount() * (intRate[0]/100/12))/1 - Math.pow(1/(1 + (intRate[0]/100/12)),loanTerm[0]*12);
				    return Payment;
			     }
 
			 catch (NumberFormatException event){
 
 
			        /*error displayed for incorrect input type*/
					  JOptionPane.showMessageDialog(null, "Incorrect Input.\nEnter numeric values.", "ERROR", JOptionPane.ERROR_MESSAGE);
				     return 0;
 
				  }
 
 
		}
 
 
		public double CalculatePayment15 (){
 
		 /*checks input for incorrect input type*/
 
		    try {
		          /*If input is coorect,then perform calculation*/
		          fieldPayment.setText ("");
				    double Payment = (loanAmount() * (intRate [1]/100/12))/1 - Math.pow(1/(1 + (intRate[1]/100/12)), loanTerm[1]*12);
				    return Payment;
			     }
 
			 catch (NumberFormatException event){
 
 
			        /*error displayed for incorrect input type*/
					  JOptionPane.showMessageDialog(null, "Incorrect Input.\nEnter numeric values.", "ERROR", JOptionPane.ERROR_MESSAGE);
				     return 0;
 
				  }
 
 
		}
 
 
      public double CalculatePayment30 (){
 
		 /*checks input for incorrect input type*/
 
		    try {
		          /*If input is coorect,then perform calculation*/
		          fieldPayment.setText ("");
				    double Payment = (loanAmount() * (intRate[2]/100/12))/1 - Math.pow(1/(1 + (intRate[2]/100/12)), loanTerm[2]*12);
				    return Payment;
			 }
 
			 catch (NumberFormatException event){
 
 
			        /*error displayed for incorrect input type*/
					  JOptionPane.showMessageDialog(null, "Incorrect Input.\nEnter numeric values.", "ERROR", JOptionPane.ERROR_MESSAGE);
				     return 0;
 
		 }
 
 
	}
 
 
 
	  public void ClearFields (){
 
	       /*make all fields blank*/
			 fieldPayment.setText ("");
			 fieldLoanAmount.setText ("");
			 areaAmTable.setText ("");
 
	}		 
 
 
	public MortCalcGUI (){
 
	       /*sets and initialize buttons*/
			 bCal7 = new JButton ("7 Year, 5.35%");
			 bCal7.setActionCommand ("Calculate7");
	         bCal15 = new JButton ("15 Year, 5.50%");
			 bCal15.setActionCommand ("Calculate15");
	         bCal30 = new JButton ("30 Year, 5.75%");
			 bCal30.setActionCommand ("Calculate30");
			 bClear = new JButton ("Reset all Fields");
			 bClear.setActionCommand ("Reset");
			 bExit = new JButton ("Exit Calculator");
			 bExit.setActionCommand ("Exit");
 
 
			 /*sets labels and field sizes for GUI*/
			 labelTitle = new JLabel ("Mortgage Calculator");
			 labelInstructions = new JLabel ("Enter loan amount and choose rate and term");
			 labelPayment = new JLabel ("Monthly Payment");
			 labelLoanAmount = new JLabel ("Amount of Loan");
			 labelAmTable = new JLabel ("Amortization Table");
			 areaAmTable = new JTextArea (10,  30);
 
			 JScrollPane scrollPane = new JScrollPane (areaAmTable, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
 
			 /*set listeners for buttons*/
			 bCal7.addActionListener(this);
			 bCal15.addActionListener(this);
             bCal30.addActionListener(this);
             bClear.addActionListener(this);
             bExit.addActionListener(this);
 
			 /*GUI constructor and set layout*/
			 JPanel mine = new JPanel ();
			 mine.setLayout (null);
 
			 mine.add (labelTitle);
			 labelTitle.setBounds (110, 30, 700, 15);
 
			 mine.add (labelInstructions);
			 labelInstructions.setBounds ( 30, 70, 450, 15);
 
			 mine.add (labelLoanAmount);
			 labelLoanAmount.setBounds (130,  110, 100, 25);
 
			 mine.add (fieldLoanAmount);
			 fieldLoanAmount.setBounds (240, 110, 100, 25);
 
 
			 mine.add (bCal7);
			 bCal7.setBounds (40, 150, 125, 30);
 
			 mine.add (bCal15);
			 bCal15.setBounds (180, 150, 125, 30);
 
			 mine.add (bCal30);
			 bCal30.setBounds (320, 200, 100, 25);
 
			 mine.add (labelPayment);
			 labelPayment.setBounds (130, 200, 100, 25);
 
			 mine.add (fieldPayment);
			 fieldPayment.setBounds (240, 200, 100, 25);
			 fieldPayment.setEditable (false);
 
			 mine.add(labelAmTable);
			 labelAmTable.setBounds (180, 250, 300, 25);
 
			 /*add scrollpane and set bounds of scrollpane*/
 
			 mine.add(scrollPane);
			 scrollPane.setBounds (50, 280, 400, 270);
			 areaAmTable.setEditable (false);
 
			 mine.add(bClear);
			 bClear.setBounds (250, 570, 125, 25);
 
			 mine.add (bExit);
			 bExit.setBounds (250, 570, 125, 30);
 
			 this.setContentPane(mine);
			 this.pack();
			 this.setTitle ("Mortgage Calculator");
 
			 /*set calculator window size*/
 
 
			 }
 
	 public double loanAmount (){
 
	         double loanAmount = Double.parseDouble(fieldLoanAmount.getText());
	         return loanAmount;
	 }	
 
 
}

Most people won't wade through elebenty gazillion lines of unformatted code. Please indicate on which line the error occurs.

The lines I am receiving errors on are in bold.

JFrame window = new MortCalcGUI();

mine.add (fieldLoanAmount);

JFrame window = new MortCalcGUI();

This line is not causing the error. It is just included in the stack trace.

mine.add (fieldLoanAmount);

This line has two likely culprits: mine and fieldLoanAmount. You can place print statements before this line to see which variable is null. Once you know which one then look through your code to find out why it is null.

Thank you. I will see if that works.