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我开发了一个带有 GUI、按钮、相关 actionListener 和异常的应用程序。今天我遇到了这个问题。在actionEvent相对于我的 GUI 的按钮中，我插入了这段代码，其中包含一些JOptionPane.showInputDialog：

public void actionPerformed(ActionEvent ae){

 if(ae.getSource()==b1){
 try{//FIRST `JOptionPane.showInputDialog`
   int load = Integer.parseInt(JOptionPane.showInputDialog(null,"Insert current load value: "));
   auto.setCurrentLoad(load);
   //other `JOptionPane.showInputDialog`
 int choiceDep = Integer.parseInt(JOptionPane.showInputDialog(null, "Does the truck transport perishable goods? 1: YES 2: NO"));
 if(choiceDep==1) {
   //here we have to insert expiration date
   int day = Integer.parseInt(JOptionPane.showInputDialog(null,"Insert value"));
  int month = Integer.parseInt(JOptionPane.showInputDialog(null,"Insert value"));
  int year = Integer.parseInt(JOptionPane.showInputDialog(null,"Insert value"));
  auto.setPerishable(day,month,year);
 }
 else if(choiceDep==2) 
                 auto.setNotPerishable();

String choiceAv = JOptionPane.showInputDialog(null, "Available Truck? Yes or no?");
 if(choiceAv.equals("Yes")) auto.setAvailable();
 else auto.setNotAvailable();

}
        //the exception      
    catch (Exception e) { System.out.println("Exception!");}             
  }

外部类的方法在哪里setAvailable, setNotAvailable,setPerishable,setCurrentLoad，有参考auto。

当我执行此代码时，它会出现 GUI，然后单击 button b1。它出现的第一个JOptionPane.showInputDialog，是插入一个存储在 a 中的值int load。

我输入了一个值，但没有JOptionPane.showInputDialog出现其他值（但还有其他输入对话框），并且在命令行中出现异常。我注意到插入的值JOptionPane.showInputDialog永远不会传递给 line auto.setCurrentLoad(load);。

为什么会这样？以前从未见过此错误。为什么我总是在第一个JOptionPane.showInputDialog可能JVM不接受JOptionPane.showInputDialog同一语句/方法中的许多异常之后立即得到异常？或者也许（我认为）是我的编程错误？

谢谢你的帮助。干杯。

编辑：我忘了插入我在命令行中得到的异常：

java.lang.NullPointerException
        at AutoCom.actionPerformed(AutoCom.java:50)
        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 So
ce)
        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.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)
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2 回答 2

1

根据您的描述，auto 变量似乎为空。

于 2011-06-29T21:44:24.267 回答
1

最有可能的是，auto在您按下按钮之前该对象未初始化。我假设auto是AutoCom该类的成员变量。在这种情况下，您可能应该将auto定义更改为：

protected <TypeOfAutoHere> auto = new <TypeOfAutoHere>();
于 2011-06-29T21:46:03.373 回答