[英]NullPointerException When Writing to a RandomAccessFile
创建后,我可以直接写入随机访问文件,但是一旦尝试从函数中写入,它就会中断。
private void openFile()
{
JFileChooser fileChooser = new JFileChooser();
fileChooser.setFileSelectionMode(JFileChooser.FILES_ONLY );
int result = fileChooser.showSaveDialog( this );
// user clicked Cancel button on dialog
if ( result == JFileChooser.CANCEL_OPTION )
{
return;
}
File fileName = fileChooser.getSelectedFile();
if ( fileName == null || fileName.getName().equals( "" ) )
{
JOptionPane.showMessageDialog( this,
"Invalid File Name",
"Invalid File Name",
JOptionPane.ERROR_MESSAGE );
}
else
{
// Open the file
try
{
RandomAccessFile output = new RandomAccessFile( fileName, "rw" );
createRecord();
}
catch ( IOException e )
{
JOptionPane.showMessageDialog( this,
"File does not exist",
"Invalid File Name",
JOptionPane.ERROR_MESSAGE );
}
}
}
private void createRecord()
{
String firstName = tfdFirst.getText();
String lastName = tfdLast.getText();
String emailAddress = tfdEmail.getText();
String homeAddress = tfdAddress.getText();
Long phoneNumber = new Long(tfdPhone.getText());
char gender = tfdGender.getText().charAt(0);
System.out.println(firstName + lastName + emailAddress + homeAddress + phoneNumber + gender);
try
{
output.seek(0);
output.writeChar(gender);
writeString( output, lastName);
writeString( output, firstName);
writeString( output, emailAddress);
writeString( output, homeAddress);
output.writeLong(phoneNumber);
}
catch(IOException ex)
{
ex.printStackTrace();
}
}
很抱歉,没有代码,但这是两个令人反感的功能。 第一种尝试在调用createRecord()
之前尝试打开一个名为output的RandomAccessFile,后者尝试将用户输入从JFrame写入文件。 如果我在createRecord()
处放一个简单的writeInt()
函数,则可以正常工作,但是一旦createRecord()
就好像输出不存在了。
我已经工作了好几个小时都无济于事,所以如果有人可以帮助找到解决方案,我将非常感激。
编辑:根据要求堆栈跟踪。 (警告,很长...)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at good_gals_customer_app.NewCustomerUI.createRecord(NewCustomerUI.java:298)
at good_gals_customer_app.NewCustomerUI.openFile(NewCustomerUI.java:273)
at good_gals_customer_app.NewCustomerUI.butCreateRecordActionPerformed(NewCustomerUI.java:186)
at good_gals_customer_app.NewCustomerUI.access$100(NewCustomerUI.java:21)
at good_gals_customer_app.NewCustomerUI$2.actionPerformed(NewCustomerUI.java:87)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6527)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6292)
at java.awt.Container.processEvent(Container.java:2234)
at java.awt.Component.dispatchEventImpl(Component.java:4883)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Component.dispatchEvent(Component.java:4705)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
at java.awt.Container.dispatchEventImpl(Container.java:2278)
at java.awt.Window.dispatchEventImpl(Window.java:2739)
at java.awt.Component.dispatchEvent(Component.java:4705)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:746)
at java.awt.EventQueue.access$400(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:697)
at java.awt.EventQueue$3.run(EventQueue.java:691)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:719)
at java.awt.EventQueue$4.run(EventQueue.java:717)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:716)
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)
您似乎有一个阴影问题...
您已经在openFile
创建了一个局部变量output
...
RandomAccessFile output = new RandomAccessFile( fileName, "rw" );
但是访问,似乎是createRecord
一个实例变量...
output.seek(0);
实例变量很可能为null
...
通常,我建议删除重新声明并使用实例字段,但是在此情况下,我认为您应该摆脱实例字段,并将RandomAccessFile
的引用传递给createRecord
方法。
您也没有在管理资源,请记住如果打开,则必须关闭它...
try (RandomAccessFile output = new RandomAccessFile( fileName, "rw" ))
{
createRecord(output);
}
catch ( IOException e )
{
JOptionPane.showMessageDialog( this,
"File does not exist",
"Invalid File Name",
JOptionPane.ERROR_MESSAGE );
}
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