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JFileChooserを追加して初期化すると、NullPointerExceptionがスローされます。 JFileChooserがなければ、コンパイルして実行するたびに同じコードがうまく実行されます。しかし、JFileChooserを追加すると例外がスローされます。時には、それが正常に実行し、時にはそれがdoesn't.Exceptionis：NullPointerException、時々実行され、例外をスローする場合があります
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)
私のコードは次のとおりです。
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();
}
}
コードバディが必要です。 – ziLk
@zilk編集済み –