使用SecureRandom时线程“AWT-EventQueue-0”中的异常java.lang.NullPointerException

Question

每次按下我正在处理的一段代码上的按钮，我都会收到以下错误。它只在我尝试使用random.nextInt（20）部分时出现，因为删除它会使它不会发生。

我想知道的是为什么我会收到此错误，以及如何解决这个问题。错误是：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at SkelePackage.SkeletonShooter$SaveListener.actionPerformed(SkeletonShooter.java:336)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$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$500(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.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)

代码本身是：

package SkelePackage;
import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.ButtonGroup;
import javax.swing.JComboBox;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.border.EtchedBorder;
import javax.swing.border.TitledBorder;
import javax.swing.JTextField;
import javax.swing.JTextArea;
import javax.swing.JScrollPane;
import java.security.SecureRandom;
import java.util.Random;
import javax.swing.JComponent;
import java.awt.event.KeyEvent;
import javax.swing.JTabbedPane;

public class SkeletonShooter extends JFrame {
  private static final int FRAME_WIDTH = 1000; //setting frame width and height
  private static final int FRAME_HEIGHT = 550;

  private static final int AREA_ROWS = 20; //setting text area width and height
  private static final int AREA_COLUMNS = 40;

  private int hitCounter = 0;
  private int critCounter = 0;
  private int totalDamage = 0;
  private int saveCounter = 0;

  private JButton shoot;
  private JButton clear;
  private JButton saveButton;

  private JCheckBox advantage;
  private JCheckBox disadvantage;
  private JCheckBox resistance;

  private JLabel skeleLabel;
  private JLabel skeleLabel2;
  private JTextField skeletons;
  private JTextField skeletons2;

  private JLabel acLabel;
  private JTextField ac;
  private JLabel dcLabel;
  private JTextField dc;

  private JLabel hitsLabel;
  private JTextField hits;

  private JLabel damLabel;
  private JTextField damage;

  private JTextArea hitsArea;
  private JTextArea damArea;

  private JLabel tHitsLabel;
  private JTextField tHitsField;

  private JLabel tDamLabel;
  private JTextField tDamField;

  private JLabel failsLabel;
  private JTextField fails;

  private JComboBox < String > comboBox;
  private JComboBox < String > comboBox2;

  private ActionListener listener;

  private SecureRandom random;
  private int roll;
  private int roll2;
  private int damRoll;
  private int save = 0;
  private skeleStats stats = new skeleStats();
  private weapon wep = new weapon();

  public SkeletonShooter() {
    JTabbedPane tabbedPane = new JTabbedPane();
    tabbedPane.add("Attack", createControlPanel());
    tabbedPane.add("Save", createFields3());
    tabbedPane.setMnemonicAt(0, KeyEvent.VK_1);
    add(tabbedPane);
    setSize(FRAME_WIDTH, FRAME_HEIGHT);
    setTitle("SkeletonShooter1.0");
  }
  public JPanel createAreas() {
    hitsArea = new JTextArea(AREA_ROWS, AREA_COLUMNS);
    hitsArea.setText("");
    hitsArea.setEditable(false);

    damArea = new JTextArea(AREA_ROWS, AREA_COLUMNS);
    damArea.setText("");
    damArea.setEditable(false);

    JPanel panel = new JPanel();
    JScrollPane scrollPane = new JScrollPane(hitsArea);
    JScrollPane scrollPane2 = new JScrollPane(damArea);
    panel.add(scrollPane);
    panel.add(scrollPane2);
    return panel;
  }

  public JPanel createFields2() {
    tHitsLabel = new JLabel("Total Hits:");
    final int FIELD_WIDTH = 10;
    tHitsField = new JTextField(FIELD_WIDTH);
    tHitsField.setText("");
    tHitsField.setEditable(false);

    tDamLabel = new JLabel("Total Damage:");
    tDamField = new JTextField(FIELD_WIDTH);
    tDamField.setText("");
    tDamField.setEditable(false);

    JPanel panel = new JPanel();
    panel.add(tHitsLabel);
    panel.add(tHitsField);
    panel.add(tDamLabel);
    panel.add(tDamField);
    return panel;

  }

  public JPanel createFields() {
    skeleLabel = new JLabel("Skeletons:");
    final int FIELD_WIDTH = 10;
    skeletons = new JTextField(FIELD_WIDTH);
    skeletons.setText("" + 0);

    acLabel = new JLabel("AC:");
    ac = new JTextField(FIELD_WIDTH);
    ac.setText("" + 0);

    JPanel panel = new JPanel();
    panel.add(skeleLabel);
    panel.add(skeletons);
    panel.add(acLabel);
    panel.add(ac);
    return panel;
  }

  public JPanel createComboBox() {
    comboBox = new JComboBox < > ();
    comboBox.addItem("Heavy Crossbow");
    comboBox.addItem("Short Sword");
    comboBox.setEditable(false);
    ActionListener comboListen = new ComboListener();
    comboBox.addActionListener(comboListen);
    comboBox.setSelectedIndex(0);
    JPanel panel = new JPanel();
    panel.add(comboBox);
    return panel;
  }

  class ComboListener implements ActionListener {
    public void actionPerformed(ActionEvent event) {
      int theIndex = comboBox.getSelectedIndex();
      if (theIndex == 0) {
        wep.setHCrossbow();
      } else if (theIndex == 1) {
        wep.setShortSword();
      }
    }
  }

  public JPanel createCheckBoxes() {
    advantage = new JCheckBox("Advantage");
    advantage.addActionListener(listener);

    disadvantage = new JCheckBox("Disadvantage");
    disadvantage.addActionListener(listener);

    resistance = new JCheckBox("Resistance");
    resistance.addActionListener(listener);

    JPanel panel = new JPanel();
    panel.add(advantage);
    panel.add(disadvantage);
    panel.add(resistance);

    return panel;
  }
  public JPanel createButtons() {
    shoot = new JButton("Fire!");
    ActionListener firelisten = new AddFireListener();
    shoot.addActionListener(firelisten);
    clear = new JButton("Clear");
    ActionListener clearlisten = new AddClearListener();
    clear.addActionListener(clearlisten);
    JPanel panel = new JPanel();
    panel.add(shoot);
    panel.add(clear);
    return panel;
  }
  class AddFireListener implements ActionListener {
    public void actionPerformed(ActionEvent event) {
      totalDamage = 0;
      hitCounter = 0;
      critCounter = 0;
      for (int n = 0; n < Integer.parseInt(skeletons.getText()); ++n) {
        roll = random.nextInt(20) + 5;
        roll2 = random.nextInt(20) + 5;
        if (advantage.isSelected() && disadvantage.isSelected()) {
          roll = roll;
        } else if (advantage.isSelected()) {
          if (roll2 > roll)
            roll = roll2;
        } else if (disadvantage.isSelected()) {
          if (roll2 < roll)
            roll = roll2;
        }
        if (roll == 24) {
          ++critCounter;
          hitsArea.append("Skeleton " + (n + 1) + " rolled a CRIT!\n");
        } else if (roll >= Integer.parseInt(ac.getText())) {
          ++hitCounter;
          hitsArea.append("Skeleton " + (n + 1) + " rolled a " + roll + " and HIT!\n");
        } else {
          hitsArea.append("Skeleton " + (n + 1) + " rolled a " + roll + " and MISSED!\n");
        }
      }
      for (int i = 0; i < hitCounter; ++i) {
        damRoll = wep.getDam();
        if (resistance.isSelected())
          damRoll = damRoll / 2;
        damArea.append("Damage from hit " + (i + 1) + ": " + damRoll + ".\n");
        totalDamage = totalDamage + damRoll;
      }
      for (int j = 0; j < critCounter; ++j) {
        damRoll = wep.getCritDam();
        if (resistance.isSelected())
          damRoll = damRoll / 2;
        damArea.append("Damage from CRIT " + (j + 1) + ": " + damRoll + ".\n");
        totalDamage = totalDamage + damRoll;
      }
      hitsArea.append("Hits: " + (hitCounter + critCounter) + "\n");
      damArea.append("Damage: " + totalDamage + "\n");
      tHitsField.setText("" + (hitCounter + critCounter));
      tDamField.setText("" + totalDamage);
    }
  }

  class AddClearListener implements ActionListener {
    public void actionPerformed(ActionEvent event) {
      hitCounter = 0;
      critCounter = 0;
      totalDamage = 0;
      hitsArea.append("Cleared!\n");
      damArea.append("Cleared!\n");
      tHitsField.setText("" + 0);
      tDamField.setText("" + 0);
      skeletons.setText("" + 0);
      ac.setText("" + 0);
    }
  }
  public JPanel createFields3() {
    skeleLabel2 = new JLabel("Skeletons:");
    final int FIELD_WIDTH = 10;
    skeletons2 = new JTextField(FIELD_WIDTH);
    skeletons2.setText("" + 0);
    skeletons2.setEditable(true);

    dcLabel = new JLabel("DC:");
    dc = new JTextField(FIELD_WIDTH);
    dc.setText("" + 0);
    dc.setEditable(true);

    comboBox2 = new JComboBox < > ();
    comboBox2.addItem("Strength");
    comboBox2.addItem("Dexterity");
    comboBox2.addItem("Constitution");
    comboBox2.addItem("Intelligence");
    comboBox2.addItem("Wisdom");
    comboBox2.addItem("Charisma");
    comboBox2.setEditable(false);
    comboBox2.setSelectedIndex(0);
    ActionListener comboListen = new ComboListener2();
    comboBox2.addActionListener(comboListen);
    comboBox2.setSelectedIndex(0);

    saveButton = new JButton("Save");
    ActionListener saveListen = new SaveListener();
    saveButton.addActionListener(saveListen);

    failsLabel = new JLabel("Fails");
    fails = new JTextField(FIELD_WIDTH);
    fails.setText("" + 0);
    fails.setEditable(false);

    JPanel panel = new JPanel();
    panel.add(skeleLabel2);
    panel.add(skeletons2);
    panel.add(dcLabel);
    panel.add(dc);
    panel.add(comboBox2);
    panel.add(saveButton);
    panel.add(failsLabel);
    panel.add(fails);

    return panel;
  }

  class ComboListener2 implements ActionListener {
    public void actionPerformed(ActionEvent event) {
      int theIndex = comboBox2.getSelectedIndex();
      if (theIndex == 0)
        save = stats.strMod();
      else if (theIndex == 1)
        save = stats.dexMod();
      else if (theIndex == 2)
        save = stats.conMod();
      else if (theIndex == 3)
        save = stats.intMod();
      else if (theIndex == 4)
        save = stats.wisMod();
      else if (theIndex == 5)
        save = stats.chaMod();
    }
  }

  class SaveListener implements ActionListener {
    public void actionPerformed(ActionEvent event) {
      saveCounter = 0;
      int roll;
      for (int q = 0; q < Integer.parseInt(skeletons2.getText()); ++q) {
        roll = random.nextInt(20) + 1 + save;
        if (roll < Integer.parseInt(dc.getText())) {
          ++saveCounter;
        }
      }
      fails.setText("" + saveCounter);
    }
  }


  public JPanel createControlPanel() {
    JPanel fields = createFields();
    JPanel cboxes = createCheckBoxes();
    JPanel areas = createAreas();
    JPanel fields2 = createFields2();
    JPanel buttons = createButtons();
    JPanel combo = createComboBox();

    JPanel controlPanel = new JPanel();
    controlPanel.add(combo);
    controlPanel.add(fields);
    controlPanel.add(cboxes);
    controlPanel.add(areas);
    controlPanel.add(fields2);
    controlPanel.add(buttons);

    return controlPanel;
  }
  public static void main(String[] args) {
    SkeletonShooter test = new SkeletonShooter();
    test.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    test.setVisible(true);

  }
}

但我相信问题出在这个方面：

    public JPanel createFields3(){
        skeleLabel2 = new JLabel("Skeletons:");
        final int FIELD_WIDTH = 10;
        skeletons2 = new JTextField(FIELD_WIDTH);
        skeletons2.setText("" + 0);
        skeletons2.setEditable(true);

        dcLabel = new JLabel("DC:");
        dc = new JTextField(FIELD_WIDTH);
        dc.setText("" + 0);
        dc.setEditable(true);

        comboBox2 = new JComboBox<>();
        comboBox2.addItem("Strength");
        comboBox2.addItem("Dexterity");
        comboBox2.addItem("Constitution");
        comboBox2.addItem("Intelligence");
        comboBox2.addItem("Wisdom");
        comboBox2.addItem("Charisma");
        comboBox2.setEditable(false);
        comboBox2.setSelectedIndex(0);
        ActionListener comboListen = new ComboListener2();
        comboBox2.addActionListener(comboListen);
        comboBox2.setSelectedIndex(0);

        saveButton = new JButton("Save");
        ActionListener saveListen = new SaveListener();
        saveButton.addActionListener(saveListen);

        failsLabel = new JLabel("Fails");
        fails = new JTextField(FIELD_WIDTH);
        fails.setText("" + 0);
        fails.setEditable(false);

        JPanel panel = new JPanel();
        panel.add(skeleLabel2);
        panel.add(skeletons2);
        panel.add(dcLabel);
        panel.add(dc);
        panel.add(comboBox2);
        panel.add(saveButton);
        panel.add(failsLabel);
        panel.add(fails);

        return panel;
    }

    class ComboListener2 implements ActionListener{
        public void actionPerformed(ActionEvent event){
            int theIndex = comboBox2.getSelectedIndex();
            if (theIndex == 0)
                save = stats.strMod();
            else if (theIndex == 1)
                save = stats.dexMod();
            else if (theIndex == 2)
                save = stats.conMod();
            else if (theIndex == 3)
                save = stats.intMod();
            else if (theIndex == 4)
                save = stats.wisMod();
            else if (theIndex == 5)
                save = stats.chaMod();  
        }
    }

    class SaveListener implements ActionListener{
        public void actionPerformed(ActionEvent event){
            saveCounter = 0;
            int roll;
            for (int q = 0 ; q < Integer.parseInt(skeletons2.getText()) ; ++q){
                roll = random.nextInt(20) + 1 + save;
                if (roll < Integer.parseInt(dc.getText())){
                    ++saveCounter;
                }
            }
            fails.setText("" +  saveCounter);
        }
    }

Answer 1

必须初始化

random：random = new SecureRandom();