Javaの課題丸投げコミュのVector

こちらのプログラム、ＧＵＩで名前、ＧＰＡ、ＡＧＥとクラスを４つ選択すると言うVectorを使った初歩なプログラムなのですが、うまくいかず困っています。
困っている部分は、jcboBoxのクラスの選択に関して。同じクラスを選択すると、JOptionPaneで警告が出されるようにしているのですが、二つ目と四つ目だけ同じクラスすると警告が出てきません（写真参照）。
どちらさまか、この解決する方法にお力のほうをお借りしたく思います。よろしくお願いします。

// ErrorAlertDemoVector.java
// gives user data input error information and allows correction
import java.awt.*;
import java.awt.event.*;
import javax.swing.*; //contains JOptionPane class
import javax.swing.border.*;
import java.util.*;

public class ErrorAlertDemoVector extends JFrame implements ActionListener {
private JLabel jlbName;
private JTextField jtfName;
private JLabel jlbAge;
private JTextField jtfAge;
private JLabel jlbGPA;
private JTextField jtfGPA;
private JLabel jlbClass1;
private JComboBox jcboClass1;
private JLabel jlbClass2;
private JComboBox jcboClass2;
private JLabel jlbClass3;
private JComboBox jcboClass3;
private JLabel jlbClass4;
private JComboBox jcboClass4;
private JButton jbtClearButton;
private JButton jbtRecordButton;
private JButton jbtRefreshButton;
private String[] classStrings = {"Select class","CS1337","CS2305","CS2336",
"CS3305","CS3335","CS3345","CS3354",
"MATH2417","MATH2419","PHYS2325","PHYS2326"};
private Vector<String> classesOffered;
private Vector<String> classesSelected;
private String name, ageString, gpaString;
private int age;
private double gpa;
private int index;

// Main method
public static void main(String[] args) {new ErrorAlertDemoVector();}

public ErrorAlertDemoVector() {
classesSelected = new Vector<String>();
classesOffered = new Vector<String>();
for(int i = 0; i < classStrings.length; i++){
classesOffered.add(classStrings[i]);
}

jlbName = new JLabel("Name:");
jtfName = new JTextField(15);
jlbAge = new JLabel("Age:");
jtfAge = new JTextField(15);
jlbGPA = new JLabel("GPA:");
jtfGPA = new JTextField(15);
jlbClass1 = new JLabel("Class 1:");
jcboClass1 = new JComboBox(classesOffered);
jlbClass2 = new JLabel("Class 2:");
jcboClass2 = new JComboBox(classesOffered);
jlbClass3 = new JLabel("Class 3:");
jcboClass3 = new JComboBox(classesOffered);
jlbClass4 = new JLabel("Class 4:");
jcboClass4 = new JComboBox(classesOffered);

// Panel labelPanel to hold labels
JPanel labelPanel = new JPanel();
labelPanel.setLayout(new GridLayout(7,1));
labelPanel.add(jlbName);
labelPanel.add(jlbAge);
labelPanel.add(jlbGPA);
labelPanel.add(jlbClass1);
labelPanel.add(jlbClass2);
labelPanel.add(jlbClass3);
labelPanel.add(jlbClass4);

JPanel fieldPanel = new JPanel();
fieldPanel.setLayout(new GridLayout(7,1));
fieldPanel.add(jtfName);
fieldPanel.add(jtfAge);
fieldPanel.add(jtfGPA);
fieldPanel.add(jcboClass1);
fieldPanel.add(jcboClass2);
fieldPanel.add(jcboClass3);
fieldPanel.add(jcboClass4);

jtfName.setText("Rocket Squirrel");
jtfAge.setText("10");
jtfGPA.setText("3.5");

JPanel dataPanel = new JPanel();
dataPanel.setLayout(new BorderLayout());
dataPanel.add(labelPanel,BorderLayout.WEST);
dataPanel.add(fieldPanel,BorderLayout.CENTER);

JPanel buttonPanel = new JPanel();
buttonPanel.setLayout(new FlowLayout());
buttonPanel.add(jbtRecordButton = new JButton("Record"));
buttonPanel.add(jbtClearButton = new JButton("Clear"));
buttonPanel.add(jbtRefreshButton = new JButton("Refresh"));

// Set border title
dataPanel.setBorder(new TitledBorder("Student Data"));

jbtRecordButton.addActionListener(this);
jbtClearButton.addActionListener(this);
jbtRefreshButton.addActionListener(this);

add(dataPanel,BorderLayout.CENTER);
add(buttonPanel,BorderLayout.SOUTH);

pack();
setTitle("Student Data");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
int screenWidth = screenSize.width;
int screenHeight = screenSize.height;

Dimension frameSize = getSize();
int x = (screenWidth - frameSize.width)/2;
int y = (screenHeight - frameSize.height)/2;

setLocation(x, y);
setVisible(true);
}

public void actionPerformed(ActionEvent e) {
if(e.getSource() == jbtRecordButton) {

name = jtfName.getText().trim();
ageString = jtfAge.getText().trim();
gpaString = jtfGPA.getText().trim();
classesSelected.clear();
classesSelected.add((String)jcboClass1.getSelectedItem());
classesSelected.add((String)jcboClass2.getSelectedItem());
classesSelected.add((String)jcboClass3.getSelectedItem());
classesSelected.add((String)jcboClass4.getSelectedItem());

//**********************************************************************
//name format error
//note: could also be done by checking for two space-delimited tokens

String[] tokens = name.split("[ ]+");
if(tokens.length < 2){
JOptionPane.showMessageDialog(null,
"Name must be at least a first and \n" +
"last name separated by a space",
"Name format warning",
JOptionPane.WARNING_MESSAGE);
return;
}

for(int i = 0; i < tokens.length; i++){
if(!isValidName(tokens[i])){
JOptionPane.showMessageDialog(null,
"Names can contain only characters and hyphens",
"Name format warning",
JOptionPane.WARNING_MESSAGE);
return;
}
}

//**********************************************************************
//number format error - age

try{
age = Integer.parseInt(ageString);

}catch(NumberFormatException nfe){
JOptionPane.showMessageDialog(null,
"Age must be an integer",
"Number format warning",
JOptionPane.WARNING_MESSAGE);
jtfAge.selectAll();
jtfAge.requestFocusInWindow();
return;
}

//**********************************************************************
//number format error - gpa

try{
gpa = Double.parseDouble(gpaString);

if(gpa < 0 || gpa > 5.0){
JOptionPane.showMessageDialog(null,
"GPA must be between 0.0 and 5.0",
"Number format warning",
JOptionPane.WARNING_MESSAGE);
jtfGPA.selectAll();
jtfGPA.requestFocusInWindow();
return;
}
}catch(NumberFormatException nfe){
JOptionPane.showMessageDialog(null,
"GPA must be an integer or a double",
"Number format warning",
JOptionPane.WARNING_MESSAGE);
jtfGPA.selectAll();
jtfGPA.requestFocusInWindow();
return;
}
//**********************************************************************
//failure to select four classes (iterator and for loop)
/*
for(index = 0; index < classesSelected.size(); index++){
if(((String)classesSelected.get(index)).equals("Select class")){
*/
Iterator<String> classIter = classesSelected.iterator();
while(classIter.hasNext()){
String classString = (String)classIter.next();
if(classString.equals("Select class")){
JOptionPane.showMessageDialog(null,
"You must select four classes!",
"Class selection warning",
JOptionPane.WARNING_MESSAGE);
return;
}
}

//**********************************************************************
//selecting the same class twice
Vector<String> tempClassesSelected = new Vector<String>(classesSelected);
for(index = 0; index < tempClassesSelected.size() - 1; index++){
String tempClass = (String)tempClassesSelected.remove(index);
if(tempClassesSelected.contains(tempClass)){
JOptionPane.showMessageDialog(null,
"You cannot select the same class twice!",
"Class selection warning",
JOptionPane.WARNING_MESSAGE);
return;
}
}
//**********************************************************************
//no exceptions
System.out.println(name);
System.out.println(age);
System.out.println(gpa);
printClasses();
}else if(e.getSource() == jbtClearButton) {
jtfName.setText("");
jtfAge.setText("");
jtfGPA.setText("");
jcboClass1.setSelectedIndex(0);
jcboClass2.setSelectedIndex(0);
jcboClass3.setSelectedIndex(0);
jcboClass4.setSelectedIndex(0);
classesSelected.clear();
}else if(e.getSource() == jbtRefreshButton) {
jtfName.setText("Rocket Squirrel");
jtfAge.setText("10");
jtfGPA.setText("3.5");
jcboClass1.setSelectedIndex(0);
jcboClass2.setSelectedIndex(0);
jcboClass3.setSelectedIndex(0);
jcboClass4.setSelectedIndex(0);
classesSelected.clear();
}
}
public void printClasses(){
Iterator iter = classesSelected.iterator();
while(iter.hasNext()){
System.out.println(iter.next());
}
}
//*****************************************************************
//Utility methods
//*****************************************************************
private boolean isValidName(String name){
return name.matches("[a-zA-Z-]+");
}
}