Eu continuo recebendo um erro de tempo de execução que diz que estou tendo uma exceção no segmento "AWT-EventQueue-0" java.lang.NullPointerException ele está dizendo um [linha 65], mas para mim ele apenas se parece com uma instrução if básica. Eu posso dar algum contexto. este quadro é chamado a partir de uma seqüência de quadros que, em seguida, é selecionada quando o estado é enviado para um novo quadro que contém estados de cidades A-C. Este quadro atual funcionará somente quando o Alabama não for o estado selecionado. (Eu não criei os outros quadros para os outros estados, por isso eles são comentados) Eu posso colocar o código no outro quadro que ele deveria chamar se alguém precisar, mas eu percebi que era um monte de código para começar com. Agradecemos antecipadamente pela ajuda a todos.

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.*;
import java.io.*;
import java.util.*;

public class WetBulbByLocationFrameStates3 extends JFrame
{
  public JLabel stateLabel;
  public JPanel statePanel = new JPanel();
  public JComboBox stateBox;
  public String [] unitedStates = {"Alabama", "Alaska", "Arizona", "Arkansas", "California", "Colorado", "Connecticut", "Delaware", "District of Columbia", "Florida", "Georgia", "Hawaii", "Idaho", "Illinois", "Indiana", "Iowa", "Kansas", "Kentucky", "Louisiana", "Maine", "Maryland", "Massachusetts", "Michigan", "Minnesota", "Mississippi", "Missouri", "Montana", "Nebraska", "Nevada", "New Hampshire", "New Jersey", "New Mexico", "New York", "North Carolina", "North Dakota", "Ohio", "Oklahoma", "Oregon", "Pennsylvania", "Rhode Island", "South Carolina", "South Dakota", "South Pacific Islands", "Tennessee", "Texas", "Utah", "Vermont", "Virginia", "Washington", "West Virginia", "Wisconsin", "Wyoming"};
  public String [] canadianProvinces = {"Alberta", "British Columbia", "Manitoba", "New Brunswick", "Newfoundland and Labrador", "Northwest Territories", "Nova Scotia", "Nunavut", "Ontario", "Prince Edward Island", "Quebec", "Saskatchewan", "Yukon Territory"};
  public JButton nextButton = new JButton("Next");
  public JPanel buttonPanel = new JPanel();
  public String state;
  public String countryGIVEN;

  public WetBulbByLocationFrameStates3(String country)
  {
    Toolkit toolkit = Toolkit.getDefaultToolkit();
    Dimension dimensions = toolkit.getScreenSize();
    int x = (dimensions.width - 315)/2; 
    int y = (dimensions.height - 250)/2;
    setBounds(x, y, 315, 250); 
    setVisible(true);
    setResizable(false);
    setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    countryGIVEN = country;

    nextButton.addActionListener(new ButtonListener3());

    if (country.equals("United States of America"))
    {
      stateBox = new JComboBox(unitedStates);
      setTitle("Select State");
      stateLabel = new JLabel("State");
    }
    else if (country.equals("Canada"))
    {
      stateBox = new JComboBox(canadianProvinces);
      setTitle("Select Province");
      stateLabel = new JLabel("Province");
    }

    stateBox.addActionListener(new ComboBoxListener2());

    statePanel.add(stateLabel);
    statePanel.add(stateBox);

    add(statePanel, BorderLayout.CENTER);

    buttonPanel.add(nextButton);

    add(buttonPanel, BorderLayout.SOUTH);
  }
  private class ButtonListener3 implements ActionListener
  {
    @Override
    public void actionPerformed(ActionEvent e)
    {
      if (countryGIVEN.equals("United States of America"))
      {
        if (state.equals("Alabama"))
        {
          JFrame wbfs1 = new WetBulbByLocationFrameStateGroupA_C(state);
        }
        else if (state.equals("Alaska"))
        {
          JFrame wbfs2 = new WetBulbByLocationFrameStateGroupA_C(state);
        }
        else if (state.equals("Arizona"))
        {
          JFrame wbfs3 = new WetBulbByLocationFrameStateGroupA_C(state);
        }
        else if (state.equals("Arkansas"))
        {
          JFrame wbfs4 = new WetBulbByLocationFrameStateGroupA_C(state);
        }
        else if (state.equals("California"))
        {
          JFrame wbfs5 = new WetBulbByLocationFrameStateGroupA_C(state);
        }
        else if (state.equals("Colorado"))
        {
          JFrame wbfs6 = new WetBulbByLocationFrameStateGroupA_C(state);
        }
        else if (state.equals("Connecticut"))
        {
          JFrame wbfs7 = new WetBulbByLocationFrameStateGroupA_C(state);
        }
      }
    }
  }
  private class ComboBoxListener2 implements ActionListener
  {
    @Override
    public void actionPerformed(ActionEvent e)
    {
      state = (String)stateBox.getSelectedItem();
    }
  }
}

PS aqui está o erro ao selecionar o Alabama.

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at WetBulbByLocationFrameStates3$ButtonListener3.actionPerformed(WetBulbByLocationFrameStates3.java:65)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$000(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)