谁能帮我识别线程“AWT-EventQueue-0"中的异常?第 65 行的 java.lang.NullPointerException? [英] Can anyone help me identify the Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException on Line 65?

问题描述

我不断收到一个运行时错误，说我在线程AWT-EventQueue-0"中有一个异常 java.lang.NullPointerException 它说的是 [line 65] 但对我来说它只是一个基本的 if 语句.我可以提供一些背景.这个帧是从一系列帧中调用的，一旦选择了状态，就会发送到包含状态 A-C 城市的新帧.仅当阿拉巴马州不是所选州时，此当前框架才会起作用.(我没有为其他状态创建其他框架，因此它们被注释掉了)我可以将代码放到另一个框架中，如果有人需要它应该调用它，但我认为这是很多代码开始和.在此先感谢大家的帮助.

I keep getting a Run Time error that says I am having an Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException it is saying a [line 65] but to me it just looks like a basic if statement. I can give some background. this frame is call from a sequence of frames that is then once the state is selected sent to a new frame that contains states A-C cities. This current frame will work only when Alabama is not the state selected. (I have not created the other frames for the other states hence why they are commented out) I can put up the code to the other frame it is supposed to call if anyone needs it but I figured that this was a lot of code to begin with. Thanks in advance for the help everybody.

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 这是选择阿拉巴马州时的错误.

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)

推荐答案

第 65 行是这个:

if (state.equals("Alabama"))

如果你看一下前面的代码，没有任何东西初始化state，所以它的值将是null.

If you look through the previous code, nothing has initialized state so its value will be null.

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