Question

我正在尝试使用简单的“提交”按钮将特定信息解析为I / O.按钮是jButton1，源textField是jTextField1（例如）。在使用Netbeans的Java UI创建中，编写了许多生成的不可编辑代码。我注意到我的ActionListener事件在这个生成的代码中;

      jButton1.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            jButton1ActionPerformed(evt);
        }
    });

接下来，我继续在这里添加了ActionPerformed和其他一些代码：

        private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         

    // Declaration of Writer I/O
    File outFile;
    FileWriter aFileWriter;
    PrintWriter aPrintWriter = null;

    // Declaration of String for Output
    String customerNumber = jTextField1.getText(); // Customer Name
    String customerSAddress = jTextField2.getText(); // Customer Street Address
    String customerCAddress = jTextField3.getText(); // Customer City
    String customerStAddress = jTextField4.getText(); // Customer State
    String customerZAddress = jTextField5.getText(); // Customer Zip Code
    String customerTelephone = jTextField9.getText(); // Customer Phone
    String productSelection = jTextField7.getText(); // 1 Desktop, 2 Laptop or 3 All-In-One
    String productQuantity = jTextField8.getText(); // Quantity

    // Creation of outputStr
        String outputStr = "Customer Name: " + customerNumber + ", " +  // CreateString            outputStr
                "Customer Address:" + customerSAddress + " " + customerCAddress +
                " " + customerStAddress + " " + customerZAddress + ", " +
                "Customer Phone Number: " + customerTelephone + ", " +
                "Customer Producton Selection: " + productSelection +  ", " +
                "Product Quantity: " + productQuantity;  // Send to FileWriter after...
        try{

            outFile = new File( "Order Information.txt", "UTF-8");
            aFileWriter = new FileWriter(outFile);
            aPrintWriter = new PrintWriter(aFileWriter);
            aPrintWriter.println(outputStr);

        }  // End try
        catch (IOException error){
            System.out.println("I/O Error, Contact Admin!");
        }  // End Catch
        finally {
            aPrintWriter.close();
        } //End Finally
    }

我的问题是......我没有语法错误，但每当我在我的控制台中按“提交”时，我有大约12种不同的错误......他们在这里：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
I/O Error, Contact Admin!
at my.RAConsultUI.RAConsultUI.jButton1ActionPerformed(RAConsultUI.java:345)
at my.RAConsultUI.RAConsultUI.access$900(RAConsultUI.java:14)
at my.RAConsultUI.RAConsultUI$10.actionPerformed(RAConsultUI.java:217)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
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.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:289)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:708)
at java.awt.EventQueue$4.run(EventQueue.java:706)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

似乎我没有正确使用Java UI语法，我是否可以让某人看到我的肩膀，并可能指出我正确的方向？

Answer 1

打印

"I/O Error, Contact Admin!"因此未找到"Order Information.txt"个文件，因此aFileWriter并且它的打印包装实例aPrintWriter仍为null，并且这就是为什么，当你试图通过在finally块中的NullPointerException实例上调用close()函数来关闭它时，你有一个null：

finally
{
   aPrintWriter.close(); // <------ here NPE, isn't it ?
}

JButton问题 - Java Netbeans NullPointerException

1 个答案: