Applet won't display in Internet Browser.

Question

import javax.swing.JTextField;
import java.util.ArrayList;
import javax.swing.*;
import java.awt.*;
import java.applet.*;
import java.awt.event.*;
public class Quiz extends JApplet implements ActionListener {
    int AnswersCorrect=0;
    JTextField textfields[] = new JTextField[18];
    JLabel labels[] = new JLabel[18];
    JLabel score = new JLabel();
    JLabel questions[] = new JLabel[18];
    JFrame frame = new JFrame();
    JScrollPane scroller = new JScrollPane(frame);
    JButton button = new JButton("Check Answers");
    GridLayout layout = new GridLayout();
    //ArrayList that will contain the User's Answers
    ArrayList<String> UsersAnswers = new ArrayList<String>(18);
    //Array of Strings that are the correct answers for the quiz
    String[] answers={
    "Answer 1 goes here",
    "Answer 2 goes here",
    "Answer 3 goes here",
    "Answer 4 goes here",
    "Answer 5 goes here",
    "Answer 6 goes here",
    "Answer 7 goes here",
    "Answer 8 goes here",
    "Answer 9 goes here",
    "Answer 10 goes here",
    "Answer 11 goes here",
    "Answer 12 goes here",
    "Answer 13 goes here",
    "Answer 14 goes here",
    "Answer 15 goes here",
    "Answer 16 goes here",
    "Answer 17 goes here",
    "Answer 18 goes here",};
public void init() {
//Makes the components
for(int ii=0;ii<questions.length; ii++){
    textfields[ii] = new JTextField();
    questions[ii] = new JLabel();
    textfields[ii].setColumns(50);
    questions[ii] = new JLabel((ii + 1) + "." + " Question" + (ii + 1) + " goes here");
    frame.add(questions[ii]);
    frame.add(textfields[ii]);
button.addActionListener(this);   
frame.add(button);
frame.add(score);
frame.setLayout(layout);
this.add(frame);
//frame.add(scroller);
frame.setVisible(true);
this.setVisible(true);
frame.setSize(500,500);
this.setSize(500,500);
public void actionPerformed(ActionEvent e){
//checks to see if button was pressed
if(e.getSource()==button){
    for(int ans=0; ans<questions.length; ans++){
    //Adds answers to the arraylist so that they can be checked
    UsersAnswers.add(textfields[ans].getText());
    //Checks for right answers
    for(int foo=0; foo<questions.length;foo++) {
        if(answers[foo].equalsIgnoreCase(UsersAnswers.get(foo))) {
        textfields[foo].setText("Correct");
        textfields[foo].setEditable(false);
        AnswersCorrect++;
         else {
        textfields[foo].setText("Incorrect");
        textfields[foo].setEditable(false);
//Displays the score
score.setText(AnswersCorrect + "/18");
}When I run this applet in a browser, I get this error:
Java Plug-in 1.6.0_13
Using JRE version 1.6.0_13 Java HotSpot(TM) Client VM
User home directory = C:\Users\Matthew
c: clear console window
f: finalize objects on finalization queue
g: garbage collect
h: display this help message
l: dump classloader list
m: print memory usage
o: trigger logging
q: hide console
r: reload policy configuration
s: dump system and deployment properties
t: dump thread list
v: dump thread stack
x: clear classloader cache
0-5: set trace level to <n>
java.lang.IllegalArgumentException: adding a window to a container
     at java.awt.Container.checkNotAWindow(Unknown Source)
     at java.awt.Container.addImpl(Unknown Source)
     at javax.swing.JViewport.setView(Unknown Source)
     at javax.swing.JScrollPane.setViewportView(Unknown Source)
     at javax.swing.JScrollPane.<init>(Unknown Source)
     at javax.swing.JScrollPane.<init>(Unknown Source)
     at Quiz.<init>(Quiz.java:16)
     at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
     at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
     at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
     at java.lang.reflect.Constructor.newInstance(Unknown Source)
     at java.lang.Class.newInstance0(Unknown Source)
     at java.lang.Class.newInstance(Unknown Source)
     at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
     at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
     at java.lang.Thread.run(Unknown Source)
Exception: java.lang.IllegalArgumentException: adding a window to a container
I am using this html code to run my applet:
*<html>*
*<head>*
*<title>Lets take a Quiz*
*</title>*
*</head>*
*<body>*
*<applet code="Quiz.class" width=500 height=500></applet>*
*</body>*
*</html>*
Does anyone know what is wrong?

Answer 1

Here is what I have now. I think I changed the things you told me to (I am probably wrong), but it is still not working.
import javax.swing.JTextField;
import java.util.ArrayList;
import javax.swing.*;
import java.awt.*;
import java.applet.*;
import java.awt.event.*;
public class Quiz extends JApplet implements ActionListener {
    int AnswersCorrect=0;
    JTextField textfields[] = new JTextField[18];
    JLabel labels[] = new JLabel[18];
    JLabel score = new JLabel();
    JLabel questions[] = new JLabel[18];
    JFrame frame = new JFrame();
    JScrollPane scroller = new JScrollPane();
    JButton button = new JButton("Check Answers");
    GridLayout layout = new GridLayout();
    JPanel panel = new JPanel();
    //ArrayList that will contain the User's Answers
    ArrayList<String> UsersAnswers = new ArrayList<String>(18);
    //Array of Strings that are the correct answers for the quiz
    String[] answers={
    "Answer 1 goes here",
    "Answer 2 goes here",
    "Answer 3 goes here",
    "Answer 4 goes here",
    "Answer 5 goes here",
    "Answer 6 goes here",
    "Answer 7 goes here",
    "Answer 8 goes here",
    "Answer 9 goes here",
    "Answer 10 goes here",
    "Answer 11 goes here",
    "Answer 12 goes here",
    "Answer 13 goes here",
    "Answer 14 goes here",
    "Answer 15 goes here",
    "Answer 16 goes here",
    "Answer 17 goes here",
    "Answer 18 goes here",};
public void init() {
//Makes the components
for(int ii=0;ii<questions.length; ii++){
    textfields[ii] = new JTextField();
    questions[ii] = new JLabel();
    textfields[ii].setColumns(50);
    questions[ii] = new JLabel((ii + 1) + "." + " Question" + (ii + 1) + " goes here");
    panel.add(questions[ii]);
    panel.add(textfields[ii]);
button.addActionListener(this);   
panel.add(button);
panel.add(score);
panel.setLayout(layout);
scroller.add(panel);
this.add(frame);
frame.getContentPane().add(scroller);
panel.setVisible(true);
frame.setVisible(true);
this.setVisible(true);
frame.setSize(500,500);
this.setSize(500,500);
public void actionPerformed(ActionEvent e){
//checks to see if button was pressed
if(e.getSource()==button){
    for(int ans=0; ans<questions.length; ans++){
    //Adds answers to the arraylist so that they can be checked
    UsersAnswers.add(textfields[ans].getText());
    //Checks for right answers
    for(int foo=0; foo<questions.length;foo++) {
        if(answers[foo].equalsIgnoreCase(UsersAnswers.get(foo))) {
        textfields[foo].setText("Correct");
        textfields[foo].setEditable(false);
        AnswersCorrect++;
         else {
        textfields[foo].setText("Incorrect");
        textfields[foo].setEditable(false);
//Displays the score
score.setText(AnswersCorrect + "/18");
}