Question

运行以下示例时，我收到NullPointerException：

private void contractExpiryActionPerformed(java.awt.event.ActionEvent evt) {                                               
   String expireDate = contractExpiry.getSelectedItem().toString();
   System.out.println(expireDate);

}

只想打印出日期以测试它是否正常工作，但无论我做什么，我都会不断收到此错误。

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at tetrapro.IncomeSolution.contractExpiryActionPerformed(IncomeSolution.java:865)
    at tetrapro.IncomeSolution.lambda$initComponents$6(IncomeSolution.java:492)
    at javax.swing.JComboBox.fireActionEvent(JComboBox.java:1258)
    at javax.swing.JComboBox.contentsChanged(JComboBox.java:1332)
    at javax.swing.JComboBox.intervalRemoved(JComboBox.java:1352)
    at javax.swing.AbstractListModel.fireIntervalRemoved(AbstractListModel.java:179)
    at javax.swing.DefaultComboBoxModel.removeAllElements(DefaultComboBoxModel.java:174)
    at javax.swing.JComboBox.removeAllItems(JComboBox.java:771)
    at tetrapro.IncomeSolution.setExpirationDates(IncomeSolution.java:250)
    at tetrapro.IncomeSolution.(IncomeSolution.java:61)
    at tetrapro.IncomeSolution.lambda$main$11(IncomeSolution.java:1007)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
    at java.awt.EventQueue.access$500(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:709)
    at java.awt.EventQueue$3.run(EventQueue.java:703)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

Answer 1

很可能contractExpiry为null getSelectedItem（）返回null。使用IDE的调试选项，并在示例代码的第3行显示断点

OR

private void contractExpiryActionPerformed(java.awt.event.ActionEvent evt) {
   System.out.println("contractExpiry = " + contractExpiry);
   System.out.println("contractExpiry.getSelectedItem() = " + contractExpiry.getSelectedItem());

   String expireDate = contractExpiry.getSelectedItem().toString();
   System.out.println(expireDate);

}

这实际上显示了NullPointerException发生的位置：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at tetrapro.IncomeSolution.contractExpiryActionPerformed(IncomeSolution.java:865)

Answer 2

 private void displayOptions(String symbol){
    int count = contractExpiry.getItemCount();

    if(count != 0){
        String expire = contractExpiry.getSelectedItem().toString();        
        x = expire.substring(expire.length()-5, expire.length());
        days = data.getDaysToExpire(symbol, x);

        displayNumDays.setText(days);

        data.getSelectedData_F(symbol, x);
    }

    String last = data.getFuturePrice(contractBox.getSelectedIndex());
    displayPrice.setText(last);

我必须测试jcombobox是否为空。当它是空的时它给了我错误。现在，如果项目计数为0，则将跳过。因此，没有更多的错误。谢谢大家的帮助。

java.lang.NullPointerException我找不到我的错误原因

2 个答案: