Java- Problem with array of objects

[Luvanime]

I am working on a lab that calculates a federal tax, state tax, and Net Pay and displays all the taxpayer's information to the screen. The Taxpayer is a class, and WeeklyTaxpayer, BiWeeklyTaxpayer, and MonthlyTaxpayer are its derived classes.

I know that my classes work fine, because I can get the program to work by declaring Taxpayer objects instead of the array.

However, the assignment requires we use a Taxpayer type array and one Taxpayer object to receive the data and display it in a JOPtionPane Dialog Box.
Whenever I execute the program, I keep getting a Null Pointer Exception.

Can anyone see what I am doing wrong? I have all my code posted.
(Oh and yes the array is supposed to be size 50, even though you can only read in 5 taxpayers.)

Main Code:

/*
 * Main.java
 *
 * Created on October 4, 2007, 2:09 AM
 *
 * To change this template, choose Tools | Template Manager
 * and open the template in the editor.
 */

package lab06b;
import javax.swing.*;
import java.text.*;

/**
 *
 * @
 */

public class Main {
    
    /** Creates a new instance of Main */
    public Main() {
    }
    
    /**
     * @param args the command line arguments
     */
    public static void main( String[] args ) {
        final int MAX_NUMBER = 5;
        Taxpayer [] taxInfo = new Taxpayer [50];
        Taxpayer t = null;
        int index = 0; // Holds index value for array variable
        DecimalFormat prec2 = new DecimalFormat("$#.00");
        DecimalFormat prec1 = new DecimalFormat("#.0%");
        String nameStr = "";   // Holds taxpayer name entered by user
        String ssNumStr = "";  // Holds taxpayer's SSNnumber as string, entered by user
        int ssNum = 0;         // Taxpayer's ssnumber as int
        char taxpayerType;      // The char form of the user-enetered taxpayer type
        String grossStr = "";  // Taxpayer's gross pay as string, entered by user
        double grossPay = 0.0; // Taxpayer's gross pay as double
        
        int count = 0;         // The number of taxpayers created
        String outputStr = ""; // String for output display to user
        String outputStr2 = "";// String for output display to user
        String msgStr = "";    // Holds message for display to user
        int resp = 0;          // User's response from showConfirmDialog method
        
        while (true) {   // Loop to input data on each taxpayer
            count++;
            
            // Read in name from user as a string
            nameStr = JOptionPane.showInputDialog("Enter taxpayer name");
            
            // Read in ID number from user as a string
            ssNumStr = JOptionPane.showInputDialog("Enter SSN number");
            // Convert from type String to type int
            ssNum = Integer.parseInt(ssNumStr.trim());
            
            // Convert from Type string to type char
            taxpayerType = getTaxpayerType();
            
            // Read in gross pay from user as a string
            grossStr = JOptionPane.showInputDialog("Enter gross pay");
            // Convert from type String to type double
            grossPay = Double.parseDouble(grossStr.trim());
            
            // Create Taxpayer instance
            switch(taxpayerType) {
                case 'W': t = new WeeklyTaxpayer(nameStr, ssNum, grossPay); break;
                case 'w': t = new WeeklyTaxpayer(nameStr, ssNum, grossPay); break;
                case 'B': t = new BiweeklyTaxpayer(nameStr, ssNum, grossPay); break;
                case 'b': t = new BiweeklyTaxpayer(nameStr, ssNum, grossPay); break;
                case 'M': t = new MonthlyTaxpayer(nameStr, ssNum, grossPay); break;
                case 'm': t = new MonthlyTaxpayer(nameStr, ssNum, grossPay); break;
            } // End of switch statement
            
            // Assignes taxpayer information to array (index) 
            taxInfo[index] = t;
           
           // Create ouputstr for each taxpayer's information
           outputStr += count + ". " + taxInfo[index].toString() + "\n";
           
           ++index; // increment array to next index 
            
            if (count < MAX_NUMBER) {
                msgStr = "\nMax number of allowed taxpayers is: " + MAX_NUMBER + "\nContinue?";
                
                resp = JOptionPane.showConfirmDialog(null, outputStr + msgStr, "Confirm",
                        JOptionPane.YES_NO_OPTION,
                        JOptionPane.QUESTION_MESSAGE);
                if (resp == JOptionPane.NO_OPTION)
                    break;
            } else {
                msgStr = "Program cannot handle any more additional taxpayers.";
                JOptionPane.showMessageDialog(null, outputStr + msgStr, "Results",
                        JOptionPane.INFORMATION_MESSAGE);
                break;
            }// End of if statement
        }// End of while loop
        
        outputStr2 = "Taxpayer list:\n";
        for (int i = 0; i <= count; i++){
            t = taxInfo[i];
            
            outputStr2 += "\n" + i + ". " + t.getName() +
                    "\n    Taxpayer Type: " + t.getClass().getName() +
                    "\n    SSN: " + t.getSSNumber() +
                    "\n    Gross Pay: " + prec2.format(t.getGrossPay()) +
                    "\n    NYS Tax: " + prec2.format(t.computeStateTax()) +
                    "\n    Fed Tax: " + prec2.format(t.computeFedTax()) +
                    "\n    Net Pay: " + prec2.format(t.computeNetPay()) + "\n"; 
        }
    
        JOptionPane.showMessageDialog(null, outputStr2, "TAXPAYERS",
                JOptionPane.INFORMATION_MESSAGE);
    }// End of main
    
    // Gets, checks, and returns character for taxpayer type
    public static char getTaxpayerType() {
        String taxpayerTypeStr;
        char type;
        
        while(true){
            // Read in letter choice for taxpayerType as a string
            taxpayerTypeStr = JOptionPane.showInputDialog(
                    "Choose taxpayer type by letter choice\n"
                    + "W - Weekly\n" + "B - Biweekly\n" + "M - Monthly");
            
            // Convert from Type string to type char
            type = taxpayerTypeStr.charAt(0);
            
            if (type == 'W' || type == 'w' || type == 'B' || type == 'b' ||
                    type == 'M' || type == 'm') {
                break;
            } else {
                JOptionPane.showMessageDialog(null,
                        "Error: Invalid Character! \nPlease input a valid character.",
                        "ERROR MESSAGE", JOptionPane.ERROR_MESSAGE);
            }
        }
        
        return(type);
    }
    
}// End of class

Netbeans is saying the exception is happening here:

outputStr2 += "\n" + i + ". " + t.getName() +

I wanted to post my classes too, but the post became too long.



EDIT:
I can't believe I didn't catch this all day, but I must have been typing the code too fast and accidentally put a <= sign in my for loop. This was looping to the 6th array variable which is null. This was creating the null exception.