когда ActionListener является каллой я получаю "Exception в потоке "АВТ-EventQueue-0" java.lang.NullPointerException"

Question

на выполнив следующий код:

import javax.swing.*; 

import java.awt.Component; 
import java.awt.Container; 
import java.awt.Dimension; 
import java.awt.FlowLayout; 

import javax.swing.AbstractButton; 
import javax.swing.Icon; 
import javax.swing.ImageIcon; 
import javax.swing.JButton; 
import javax.swing.JFileChooser; 
import javax.swing.JFrame; 
import javax.swing.JTextField; 

import matlabcontrol.MatlabConnectionException; 
import matlabcontrol.MatlabInvocationException; 

import java.awt.*; 
import java.awt.event.*; 
import java.io.IOException; 
import java.lang.reflect.InvocationTargetException; 

import com.jgoodies.forms.layout.FormLayout; 
import com.jgoodies.forms.layout.ColumnSpec; 
import com.jgoodies.forms.factories.FormFactory; 
import com.jgoodies.forms.layout.RowSpec; 

class BackgroundImageJFrame1 extends JFrame { 
    public BackgroundImageJFrame1() { 
     JLabel l1_1; 
     JFileChooser fc = null; 
     final JTextField textField; 
     final JButton jb1 = null; 

     // getContentPane().setLayout(new BorderLayout()); 
     // setContentPane(new JLabel(new ImageIcon("Car-1202184041.png"))); 
     // getContentPane().setLayout(new FlowLayout()); 

     JFrame Frame1 = new JFrame(); 
     // Just for refresh :) Not optional! 
     Frame1.setSize(399, 399); 
     setSize(400, 400); 

     Frame1.setTitle("Parallel Session"); 
     Frame1.setSize(400, 400); 
     Frame1.setLocationRelativeTo(null); 
     Frame1.setDefaultCloseOperation(EXIT_ON_CLOSE); 
     Frame1.setVisible(true); 

     final JPanel panel1 = new JPanel(); 
     panel1.setLayout(new FormLayout(new ColumnSpec[] { 
       ColumnSpec.decode("132px"), 
       FormFactory.LABEL_COMPONENT_GAP_COLSPEC, 
       ColumnSpec.decode("63px"), FormFactory.UNRELATED_GAP_COLSPEC, 
       ColumnSpec.decode("28px"), 
       FormFactory.LABEL_COMPONENT_GAP_COLSPEC, 
       ColumnSpec.decode("91px"), }, new RowSpec[] { 
       RowSpec.decode("23px"), FormFactory.LINE_GAP_ROWSPEC, 
       RowSpec.decode("20px"), FormFactory.LINE_GAP_ROWSPEC, 
       RowSpec.decode("23px"), FormFactory.LINE_GAP_ROWSPEC, 
       RowSpec.decode("28px"), RowSpec.decode("23px"), 
       FormFactory.RELATED_GAP_ROWSPEC, FormFactory.DEFAULT_ROWSPEC, 
       RowSpec.decode("22px"), RowSpec.decode("14px"), })); 

     l1_1 = new JLabel("Parallel Simulation Model"); 
     panel1.add(l1_1, "1, 1, 7, 1, center, top"); 
     l1_1.setForeground(Color.RED); 
     l1_1.setFont(new Font("Palatino Linotype", Font.BOLD, 16)); 
     l1_1.setToolTipText("Getting Started"); 
     l1_1.setBounds(86, 54, 219, 45); 

     // Icon image = new ImageIcon("Car-1202184041.png"); 
     // panel1.add((Component) image); 

     JLabel j1 = new JLabel("Select your model"); 
     panel1.add(j1, "1, 3, right, center"); 
     JTextField jt1 = new JTextField(); 

     jt1.setPreferredSize(new Dimension(160, 20)); 
     panel1.add(jt1, "3, 3, 5, 1, left, top"); 
     // System.out.println("boom"); 
     JButton jb11 = new JButton("Browse"); 
     jb11.setPreferredSize(new Dimension(100, 20)); 
     panel1.add(jb11, "3, 5, 3, 1, right, center"); 

     jb11.addActionListener(new java.awt.event.ActionListener() { 
      @Override 
      public void actionPerformed(java.awt.event.ActionEvent evt) { 
       btnBrowseActionPerformed(null); 
      } 

     }); 
     JButton jb2 = new JButton("OK"); 
     panel1.add(jb2, "7, 5, left, top"); 

     jb2.addActionListener(new java.awt.event.ActionListener() { 
      @Override 
      public void actionPerformed(java.awt.event.ActionEvent arg0) { 

       try { 
        multi m = new multi(); 
       } catch (InvocationTargetException | InterruptedException 
         | MatlabConnectionException | MatlabInvocationException e) { 
        // TODO Auto-generated catch block 
        e.printStackTrace(); 
       } 
      } 

     }); 
     // System.out.println("boom"); 
     JLabel label1 = new JLabel("Enter the number of instances"); 
     panel1.add(label1, "1, 7, 1, 2, left, center"); 
     // System.out.println("boom"); 
     Frame1.setVisible(true); 
     Frame1.setSize(300, 300); 
     // System.out.println("boom"); 
     Frame1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     Frame1.getContentPane().add(panel1); 
     panel1.setBackground(Color.gray); 

     final JSpinner spinner = new JSpinner(); 
     panel1.add(spinner, "3, 7, 3, 1"); 

     JButton b11 = new JButton("SET"); 
     panel1.add(b11, "7, 7, left, top"); 

     JProgressBar progressBar = new JProgressBar(); 
     progressBar.setValue(1); 
     progressBar.setIndeterminate(true); 
     panel1.add(progressBar, "3, 10, 4, 1"); 

     // done 

     b11.addActionListener(new ActionListener() { 
      public void actionPerformed(ActionEvent arg0) { 
       String a = (String) spinner.getValue(); 
       System.out.println(" " + a); 
       try { 
        int itr = Integer.parseInt(a); 
        for (int i = 1; i <= itr; i++) { 
         multi m = new multi(); 
         System.out.println("qweqwe"); 
         JLabel l1 = new JLabel("MANUEVER DETAILS"); 
         JTextField p = new JTextField("Enter the manuever here"); 
         panel1.add(l1); 
         panel1.add(p); 
        } 
       } catch (InvocationTargetException | InterruptedException 
         | MatlabConnectionException | MatlabInvocationException e) { 
        // TODO Auto-generated catch block 
        ((Throwable) e).printStackTrace(); 
       } 

      } 
     }); 

    } 

    private void add(ImageIcon image) { 
     // TODO Auto-generated method stub 

    } 

    private void btnBrowseActionPerformed(ActionListener evt) { 

     Object fc = null; 
     if (fc == null) { 
      fc = new JFileChooser(); 
     } 

     // Show it. 
     int returnVal = ((JFileChooser) fc).showOpenDialog(null); 

     AbstractButton textField = null; 
     // Process the results. 
     if (returnVal == JFileChooser.APPROVE_OPTION) { 
      textField.setText(((JFileChooser) fc).getSelectedFile().getPath()); 
     } else { 
      textField.setText(""); 
     } 

     // Reset the file chooser for the next time it's shown. 
     ((JFileChooser) fc).setSelectedFile(null); 

    } 

    public static void main(String[] args) throws MatlabConnectionException, 
      MatlabInvocationException, IOException { 

     EventQueue.invokeLater(new Runnable() { 

      @Override 
      public void run() { 
       try { 
        System.out.println("hey"); 

        new BackgroundImageJFrame1(); 
       } catch (Exception e) { 
        e.printStackTrace(); 
       } 
      } 

     }); 

    } 
} 

Я получаю следующие результаты:

эй

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException 
    at BackgroundImageJFrame1.btnBrowseActionPerformed(BackgroundImageJFrame1.java:180) 
    at BackgroundImageJFrame1.access$0(BackgroundImageJFrame1.java:165) 
    at BackgroundImageJFrame1$1.actionPerformed(BackgroundImageJFrame1.java:90) 
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) 
    at javax.swing.AbstractButton$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 Source) 
    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.dispatchEventImpl(Unknown Source) 
    at java.awt.EventQueue.access$300(Unknown Source) 
    at java.awt.EventQueue$3.run(Unknown Source) 
    at java.awt.EventQueue$3.run(Unknown Source) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) 
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source) 
    at java.awt.EventQueue$4.run(Unknown Source) 
    at java.awt.EventQueue$4.run(Unknown Source) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(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) 

Answer 1

Его из-за следующих:

AbstractButton textField = null; 
    // Process the results. 
    if (returnVal == JFileChooser.APPROVE_OPTION) { 
     textField.setText(((JFileChooser) fc).getSelectedFile().getPath()); 
    } else { 
     textField.setText(""); 
    } 

Вы пытаетесь установить текст в ссылке null. Вы можете использовать что-то вроде:

AbstractButton textField = new JButton();// or any other class object which you want 

Answer 2

Вы устанавливаете текстовое поле пустое значение:

AbstractButton textField = null; 
    // Process the results. 
    if (returnVal == JFileChooser.APPROVE_OPTION) { 
     textField.setText(((JFileChooser) fc).getSelectedFile().getPath()); 
    } else { 
     textField.setText(""); 
    } 

И после того, что вы называете setText() и это вызовет NPE.

Так я думаю, что вы должны изменить'final JTextField TextField; 'к переменной класса и удалить строку AbstractButton textField = null;