Input/Output And Method Not Found Problem

Question

Ok so firstly I think I should apologise on two fronts.
Firstly, 'cause this is probably posted in the wrong board but I'm not sure this was suitable for the Swing board just 'cause I've been using Swing? And secondly 'cause the code I'm gonna post is so shoddy I would think this constitutes as flaim-bait. >_>
In my defense this is purely for a little class project to give something to write some documentation on so I'm really not too bothered about the efficiency or ace-mazingness of the end result. I just want it to work.
To the problem at hand.
I'm trying to write a program that asks the user a question and then outputs their answer to a file, from which a tally of answers can later be made for the purpose of displaying "results".
My problem is I've been having problems with the input/output of saving the answers given to the program.
I'm still learning and input/output is probably my weakest subject (other than, y'know, being good at Java). I've had a bash at it in the following code but all it does it overwrite what is in the file with a single answer so no list of results accumulate. I generally don't have an idea what to try for that one so any pointers would be appreciated.
Also, my second problem is, in trying to gather results by tallying what is contained in the file, I've run across a problem with the charAt() method not being found and I'm not sure why. Isn't that method a part of java.lang?
Here's the code thus far:
//libraries
import javax.swing.*;
import javax.swing.border.*;
import javax.swing.text.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
import java.text.*;
import java.io.*;
class CaseStudy {
     public static void main(String args[]) {
          GUI maininterface = new GUI();
          maininterface.setupMenu();
          maininterface.display();
class GUI {
     //for the actionlisteners
     int whatframe = 0;
     //creates mainframe and border content panel
     JFrame mainframe = new JFrame("Survey Client");
     JPanel borderpanel = new JPanel(), bottompanel = new JPanel();
     JButton quizbutton = new JButton("Take the quiz"), tallybutton = new JButton("Show Results"), submitbutton = new JButton("Submit Results"), menubutton = new JButton("Return To Menu");
     QuizQuestions toppanel = new QuizQuestions();
     QuizResults toppanel2 = new QuizResults();
     GUI() {
          //sets border in borderpanel, this spaces the main content in from the sides of the window
          borderpanel.setBorder(BorderFactory.createEmptyBorder(10,10,10,10));
          //sets up the frame and panels and adds on borders
          mainframe.setDefaultCloseOperation(mainframe.EXIT_ON_CLOSE); // exits java when clicking on close on main frame
          mainframe.getContentPane().add(borderpanel); // adds the panel as a component to the frame, the panel can hold stuffs
          borderpanel.setLayout(new BoxLayout(borderpanel, BoxLayout.PAGE_AXIS));// page_axis means it'll layout vertically
          bottompanel.setLayout(new BoxLayout(bottompanel, BoxLayout.LINE_AXIS));// line_axis means it'll layout horizontally
          //gives button an action
          quizbutton.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e1) {
                    setupQuiz();
          tallybutton.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e1) {
                    if(whatframe == 1) setupResults();
                    else {
                         int rusure = JOptionPane.showConfirmDialog(null, "Are you sure you wish to show results? Any current quiz answers won't be saved.", "Please Choose One", JOptionPane.YES_NO_OPTION);
                         if(rusure == JOptionPane.YES_OPTION) setupResults();
          menubutton.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e1) {
                    setupMenu();
          submitbutton.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e1) {
                    toppanel.doQuiz();
          borderpanel.add(bottompanel);
     public void setupMenu() {
          if(whatframe == 3) {
               bottompanel.remove(menubutton);
               borderpanel.remove(toppanel2);
          whatframe = 1;
          //adds components and lays them out
          bottompanel.add(quizbutton);
          bottompanel.add(Box.createRigidArea(new Dimension(0,10)));
          bottompanel.add(tallybutton);
          display();
     public void setupQuiz() {
          bottompanel.remove(quizbutton);
          bottompanel.remove(Box.createRigidArea(new Dimension(0,10)));
          bottompanel.remove(tallybutton);
          whatframe = 2;
          bottompanel.add(submitbutton);
          bottompanel.add(Box.createRigidArea(new Dimension(0,10)));
          bottompanel.add(tallybutton);
          borderpanel.add(toppanel);
          display();
     public void setupResults() {
          if(whatframe == 1) {
               bottompanel.remove(quizbutton);
               bottompanel.remove(Box.createRigidArea(new Dimension(0,10)));
               bottompanel.remove(tallybutton);
          else {
               bottompanel.remove(submitbutton);
               bottompanel.remove(Box.createRigidArea(new Dimension(0,10)));
               bottompanel.remove(tallybutton);
               borderpanel.remove(toppanel);
          whatframe = 3;
          bottompanel.add(menubutton);
          borderpanel.add(toppanel2);
          display();
     public void display() {
          //sets the size of the frame around it's components and then shows it
          mainframe.pack();
          mainframe.setVisible(true);
          mainframe.validate(); //makes referenced container relayout it's components
class QuizQuestions extends JPanel {
     LoadingSaving loadsave = new LoadingSaving();
     JPanel popm = new JPanel(), pop1 = new JPanel(), pop2 = new JPanel(), pop3 = new JPanel(), pop4 = new JPanel();
     JFormattedTextField ques = new JFormattedTextField(), op1 = new JFormattedTextField(), op2 = new JFormattedTextField(), op3 = new JFormattedTextField(), op4 = new JFormattedTextField();
     JButton bop1 = new JButton("1"), bop2 = new JButton("2"), bop3 = new JButton("3"), bop4 = new JButton("4");
     char answer;
     QuizQuestions() {
          popm.setLayout(new BoxLayout(popm, BoxLayout.PAGE_AXIS));
          pop1.setLayout(new BoxLayout(pop1, BoxLayout.LINE_AXIS));
          pop2.setLayout(new BoxLayout(pop2, BoxLayout.LINE_AXIS));
          pop3.setLayout(new BoxLayout(pop3, BoxLayout.LINE_AXIS));
          pop4.setLayout(new BoxLayout(pop4, BoxLayout.LINE_AXIS));
          this.add(popm);
          popm.add(ques);
          popm.add(pop1);
          popm.add(pop2);
          popm.add(pop3);
          popm.add(pop4);
          pop1.add(op1);
          pop1.add(bop1);
          pop2.add(op2);
          pop2.add(bop2);
          pop3.add(op3);
          pop3.add(bop3);
          pop4.add(op4);
          pop4.add(bop4);
          //sets up question text fields
          ques.setEditable(false);
          op1.setEditable(false);
          op2.setEditable(false);
          op3.setEditable(false);
          op4.setEditable(false);
          bop1.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e1) {
                    answer = 'a';
          bop2.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e1) {
                    answer = 'b';
          bop3.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e1) {
                    answer = 'c';
          bop4.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e1) {
                    answer = 'd';
          Question1();
     public void doQuiz() {
          loadsave.save(answer);
     public void Question1() {
          ques.setValue("Who's your favourite X-Men character?");
          op1.setValue("Cyclops");
          op2.setValue("Xavier");
          op3.setValue("Wolverine");
          op4.setValue("Rogue");
class QuizResults extends JPanel {
     LoadingSaving loadsave = new LoadingSaving();
     JPanel popm = new JPanel();
     JFormattedTextField op1 = new JFormattedTextField(), op2 = new JFormattedTextField(), op3 = new JFormattedTextField(), op4 = new JFormattedTextField();
     int[] answerarray = new int[4];
     QuizResults() {
          popm.setLayout(new BoxLayout(popm, BoxLayout.PAGE_AXIS));
          this.add(popm);
          popm.add(op1);
          popm.add(op2);
          popm.add(op3);
          popm.add(op4);
          op1.setEditable(false);
          op2.setEditable(false);
          op3.setEditable(false);
          op4.setEditable(false);
          answerarray = loadsave.load();
          op1.setValue(answerarray[0]);
          op2.setValue(answerarray[1]);
          op3.setValue(answerarray[2]);
          op4.setValue(answerarray[3]);
class LoadingSaving {
     public void save(char answer) {
          FileReader fr;
          FileWriter fw;
          BufferedReader br;
          String s;
          try {
          //ERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERROR
               fr = new FileReader("casestudyoutput.txt");
               fw = new FileWriter("casestudyoutput.txt");
               br = new BufferedReader(fr);
               if (br.readLine() == null) s = "x";
               else s = br.readLine();
               s = s + answer;
               fw.write(s);
               fr.close();
               fw.close();
          //ERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERROR
          catch(FileNotFoundException exc) {
               JOptionPane.showMessageDialog(null, "File not found.");
               return;
          catch(IOException exc) {
               JOptionPane.showMessageDialog(null, "Something bad happened.");
               return;
     public int[] load() {
          FileReader fr;
          BufferedReader br;
          int[] answerarray = new int[3];
          String s;
          long length;
          int a = 0, b = 0, c = 0, d = 0;
          answerarray[0] = 0;
          answerarray[1] = 0;
          answerarray[2] = 0;
          answerarray[3] = 0;
          try {
               fr = new FileReader("casestudyoutput.txt");
               br = new BufferedReader(fr);
               if (br.readLine() == null) return answerarray;
               else s = br.readLine();
               length = s.length();
               for(int i = 0; i < length; i++) {
                    char ch = charAt(i); //ERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERRORERROR
                    switch(ch) {
                         case 'a':
                              a++;
                              break;
                         case 'b':
                              b++;
                              break;
                         case 'c':
                              c++;
                              break;
                         case 'd':
                              d++;
                              break;
               answerarray[0] = a;
               answerarray[1] = b;
               answerarray[2] = c;
               answerarray[3] = d;
               fr.close();
          catch(FileNotFoundException exc) {
               JOptionPane.showMessageDialog(null, "File not found.");
               return answerarray;
          catch(IOException exc) {
               JOptionPane.showMessageDialog(null, "Something bad happened.");
               return answerarray;
     return answerarray;
}Any pointers/tips/solutions/angry posts to tell me to stop trying to learn Java would be greatly appreciated.
Thanks in advance!
Oh, and in trying to work with it a bit further I realised I'm having a few problems with runtime errors due to exceptions. The first was due to the array being assigned out of bounds (fixed in the above code). But the second reads the following:
Exception in thread "main" java.lang.NullPointerException
     at Loadingsaving.load(CaseStudy.java:330)
     at QuizResults.(init)(CaseStudy.java.259)
     at GUI.(init)(CaseStudy.java:34)
     at CaseStudy.main(CaseStudy.java:15)Not quite sure what this one means or how to handle it. =\
Edited by: ThePermster on May 19, 2008 8:08 AM

Answer 1

A NullPointerException means a method has been called on a null object, or a variable that isn't pointing to any object. Your Exception points to line 330, which is:
length = s.length();A NPE on that line means that s is null. So let's look at where s is set:
if (br.readLine() == null) return answerarray;
else s = br.readLine();s gets it's value from br.readLine(), so that method must be returning null. You have a logical error here. Look at your If-Else. It reads a line, makes sure it isn't null...then it reads another line. Well what if that line is null? You are performing 2 reads here instead of 1.
Since your If condition returns a value, there's no need for an Else. The code will continue on until it reaches another return. Try this:
s = br.readLine();
if (s == null) return answerarray;