Sigo recibiendo un error en el Tiempo de Ejecución que dice que estoy teniendo una Excepción en el subproceso "AWT-EventQueue-0" java.lang.NullPointerException está diciendo una [línea 65] pero para mí solo se ve como una declaración if básica. Puedo dar algunos antecedentes. este marco se llama desde una secuencia de marcos que, una vez que se selecciona el estado, se envía a un nuevo marco que contiene los estados A-C de las ciudades. Este marco actual solo funcionará cuando Alabama no sea el estado seleccionado. (No he creado los otros marcos para los otros estados, por lo tanto, la razón por la que están comentados) Puedo colocar el código en el otro marco al que se supone que debe llamar si alguien lo necesita, pero pensé que era un montón de código para comenzar. con. Gracias de antemano por la ayuda 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();
    }
  }
}

PD: aquí está el error al seleccionar 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)