显示java.lang.NullPointerException我找不到我的错误，为什么

-3

运行下面的例子，当我得到一个NullPointerException：显示java.lang.NullPointerException我找不到我的错误，为什么

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

}

只想打印出日期，以测试它是否工作，但无论我做什么，我都会收到这个错误。

 
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)

来源

2016-10-22 Philip Caputo

什么是'contractExpiry'？ – gschambial

contractExpiry是一个JcomboBox。我知道nullPointerException是什么。我不知道它为什么显示在我的代码中。这没有任何意义。我在构造函数中有eventListener，但是当我想要选择该项时，我总是得到这个错误。 –

最可能的contractExpiry为null getSelectedItem（）返回null。使用IDE的调试选项和您的示例代码中的3号线订货量大的断点

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); 

}

这实际上显示了其中NullPointerException异常发生：

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

来源

2016-10-28 14:31:08

我明白了。谢谢 –

是否没有选择任何项目？ –

我让这个方法取一个参数然后解决它。 –

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，它给了我错误。现在，如果项目计数为0，它将跳过。因此，没有更多的错误。谢谢大家的帮助。

来源

2016-10-31 01:12:40

显示java.lang.NullPointerException我找不到我的错误，为什么

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