NullPointerException, manchmal wird es ausgeführt und manchmal löst es Ausnahme

Question

Wenn ich JFileChooser hinzufügen und initialisieren, wird die NullPointerException ausgelöst. Ohne JFileChooser läuft derselbe Code jedes Mal, wenn ich kompiliere und laufe, ziemlich gut. Aber wenn ich JFileChooser hinzufüge, löst es die Ausnahme aus. Manchmal läuft es erfolgreich und manchmal doesn't.Exceptionis es:

Exception in thread "main" java.lang.NullPointerException 
at javax.swing.text.PlainView.getPreferredSpan(PlainView.java:233) 
at javax.swing.plaf.basic.BasicTextUI$RootView.getPreferredSpan(BasicTextUI.java:1353) 
at javax.swing.plaf.basic.BasicTextUI.getPreferredSize(BasicTextUI.java:921) 
at  javax.swing.plaf.basic.BasicTextAreaUI.getPreferredSize(BasicTextAreaUI.java:120) 
at javax.swing.JComponent.getPreferredSize(JComponent.java:1659) 
at javax.swing.JTextArea.getPreferredSize(JTextArea.java:619) 
at javax.swing.ScrollPaneLayout.layoutContainer(ScrollPaneLayout.java:791) 
at java.awt.Container.layout(Container.java:1508) 
at java.awt.Container.doLayout(Container.java:1497) 
at java.awt.Container.validateTree(Container.java:1693) 
at java.awt.Container.validateTree(Container.java:1702) 
at java.awt.Container.validateTree(Container.java:1702) 
at java.awt.Container.validateTree(Container.java:1702) 
at java.awt.Container.validateTree(Container.java:1702) 
at java.awt.Container.validate(Container.java:1628) 
at java.awt.Container.validateUnconditionally(Container.java:1665) 
at java.awt.Window.show(Window.java:1033) 
at java.awt.Component.show(Component.java:1654) 
at java.awt.Component.setVisible(Component.java:1606) 
at java.awt.Window.setVisible(Window.java:1014) 
at notepad.Notepad.<init>(Notepad.java:66) 
at notepad.Notepad.main(Notepad.java:144) 

Mein Code ist:

package notepad; 

import java.awt.Color; 
import java.awt.Font; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import java.io.FileNotFoundException; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import javax.swing.ImageIcon; 
import javax.swing.JFileChooser; 
import javax.swing.JFrame; 
import javax.swing.JMenu; 
import javax.swing.JMenuBar; 
import javax.swing.JMenuItem; 
import javax.swing.JOptionPane; 
import javax.swing.JScrollPane; 
import javax.swing.JTextArea; 


public class Notepad extends JFrame implements ActionListener{ 
private JTextArea area; 
private ImageIcon frameicon; 
private JMenu filemenu; 
private JMenu editmenu; 
private JMenu formatmenu; 
private JMenu helpmenu; 
private JScrollPane scroll; 
private Font font; 
private JMenuBar menubar; 
private JMenuItem newmenuitem; 
private JMenuItem openmenuitem; 
private JMenuItem savemenuitem; 
private JMenuItem exitmenuitem; 
private int msg; 
private int returnVal; 
private JFileChooser choose; 


public Notepad(){ 
    initComponents(); 
    setComponents(); 

    setTitle("Simple Notepad"); 
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    setLocation(500, 100); 
    setResizable(true); 
    setSize(600,600); 
    setJMenuBar(menubar); 



    menubar.add(filemenu); 
    menubar.add(editmenu); 
    menubar.add(formatmenu); 
    menubar.add(helpmenu); 
    filemenu.add(newmenuitem); 
    filemenu.add(openmenuitem); 
    filemenu.add(savemenuitem); 
    filemenu.add(exitmenuitem); 


    add(scroll); 
    setIconImage(frameicon.getImage()); 
    setVisible(true); 
} 


public final void initComponents(){ 
    area = new JTextArea(); 
    scroll = new JScrollPane (area, //no need of add textArea when added in  JScrollPane 
    JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS); 
    menubar = new JMenuBar(); 
    filemenu = new JMenu(" File"); 
    editmenu = new JMenu(" Edit"); 
    formatmenu = new JMenu(" Format"); 
    helpmenu = new JMenu(" Help"); 
    newmenuitem = new JMenuItem(" New"); 
    openmenuitem = new JMenuItem(" Open"); 
    savemenuitem = new JMenuItem(" Save"); 
    exitmenuitem = new JMenuItem(" Exit"); 
    choose = new JFileChooser("E:"); 
    font = new Font("Calibri",Font.PLAIN,26); 
    frameicon = new ImageIcon(getClass().getResource("/res/setting.png")); 
} 

public final void setComponents(){ 

    area.setSize(600,600); 
    area.setBackground(Color.WHITE); 
    area.setFont(font); 
    //adding ActionListener 
    newmenuitem.addActionListener(this); 
    exitmenuitem.addActionListener(this); 
    openmenuitem.addActionListener(this); 

} 
@Override 
public void actionPerformed(ActionEvent e){ 

    //if newmenuitemclicked 
    if(e.getSource()==newmenuitem) { 
     if(area.getText()!=""){ 
      msg = JOptionPane.showConfirmDialog(menubar, "DO you want to save changes?"); 
      if(msg == JOptionPane.YES_OPTION){ 
       try { 

        FileOutputStream file = new FileOutputStream("E:\\newdocument.txt"); 
        String s = area.getText(); 
        byte c[] = s.getBytes(); 
        file.write(c); 
        area.setText(""); 
        JOptionPane.showMessageDialog(menubar, "File saved as E:\\newdocument.txt"); 
        file.close(); 

       } catch (FileNotFoundException ex) { 

       } catch (IOException ex) { 

       } 
      } 
      if(msg == JOptionPane.NO_OPTION){ 

      } 

     } 

    } 

    if(e.getSource() == exitmenuitem){ 
     msg = JOptionPane.showConfirmDialog(menubar, "Are you sure you want to exit?"); 
     if(msg == JOptionPane.YES_OPTION) 
     System.exit(0); 

} 
    if(e.getSource() == openmenuitem){ 

    } 

} 

public static void main(String[] args) { 
    Notepad n = new Notepad(); 
} 
} 

Answer 1

keine Relevanz für JFileChooser denke ich. Scheint, dass eine Ihrer Komponenten nicht ordnungsgemäß instanziiert wurde.

at java.awt.Window.setVisible(Window.java:1014) 

Und Sie können seine setVisible(true) Methode nicht aufrufen.
Wie auch immer, um die wahre Ursache zu erkennen, sollten Sie Ihren Code einschließen.

---

Update: da Ihr Code enthalten ist, können Sie nicht setVisible Methode in Konstruktor verwenden. Verwenden Sie es in init() Methode.
Das liegt daran, dass Ihr Objekt nicht ordnungsgemäß instanziert wird, bevor die Konstruktorfunktion beendet wird.