Я получаю сообщение об ошибке выполнения, в котором говорится, что у меня возникла исключительная ситуация в потоке & quot; AWT-EventQueue-0 & quot; java.lang.NullPointerException это говорит о [строка 65], но для меня это просто выглядит как базовый оператор if. Я могу дать некоторую предысторию. этот кадр является вызовом из последовательности кадров, которая затем после выбора состояния отправляется в новый кадр, который содержит города A-C состояний. Этот текущий кадр будет работать только тогда, когда штат Алабама не выбран штат. (Я не создал другие фреймы для других состояний, поэтому они закомментированы). Я могу поместить код в другой фрейм, который он должен вызывать, если кому-то это нужно, но я подумал, что это было много кода для начала с. Заранее спасибо всем за помощь.

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 here's the error when selecting 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)