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你好這是我創造，我有這個錯誤我的第一個Java應用程序我有一種感覺，這是一個語法錯誤，但我不能找到它，即使我在C++錯誤與我的Java的記事本
/**********************************
Notepad Created By Anmol Brar
Free To Be Copied & Modified
www.github.com/anmol-brar
www.twitter.com/circlinq_anmol
**********************************/
package com.anmol.notepad;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.InputEvent;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import javax.swing.JColorChooser;
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;
import javax.swing.KeyStroke;
import javax.swing.ScrollPaneConstants;
public class Notepad extends JFrame implements ActionListener {
// DEFINING MENUBAR
JMenuBar mb;
JMenu filemenu, editmenu, formatmenu, viewmenu, helpmenu;
JMenuItem newitem, openitem, saveitem, saveasitem, pagesetupitem, printitem, exititem, undoitem, cutitem, copyitem,
pasteitem, deleteitem, finditem, findnextitem, replaceitem, gotoitem, selectallitem, timeanddateitem,
wordwrapitem, fontitem, statusbaritem, viewhelpitem, aboutnotepaditem;
// CATEGORIZING MENUBAR SHORTCUT NAMES
JTextArea ta;
JScrollPane jsp;
JFileChooser jfc;
JColorChooser jc;
// DEFINING FONT
Font f = new Font("calbri", 4, 30);
// CONSTRUCTOR
public Notepad() {
jfc = new JFileChooser();
jc = new JColorChooser();
ta = new JTextArea();
ta.setFont(f);
// MAKING SCROLLPANES
int vsp = ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS;
int hsp = ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS;
jsp = new JScrollPane(ta, vsp, hsp);
add(jsp);
// DEFINING MENUBAR/MAKING
mb = new JMenuBar();
setJMenuBar(mb);
filemenu = new JMenu("File");
filemenu = new JMenu("Edit");
filemenu = new JMenu("Format");
filemenu = new JMenu("View");
filemenu = new JMenu("Help");
// CREATING ITEMS
mb.add(filemenu);
mb.add(editmenu);
mb.add(formatmenu);
mb.add(viewmenu);
mb.add(helpmenu);
newitem = new JMenuItem("New");
newitem.setAccelerator(KeyStroke.getKeyStroke('N', 1));
openitem = new JMenuItem("Open");
saveitem = new JMenuItem("Save");
saveasitem = new JMenuItem("Save This File As....");
pagesetupitem = new JMenuItem("Page Setup");
printitem = new JMenuItem("Print This Document(Ctrl + P)");
exititem = new JMenuItem("Exit This Document/Program :(");
exititem.setAccelerator(KeyStroke.getKeyStroke('X', InputEvent.ALT_DOWN_MASK));
undoitem = new JMenuItem("Undo");
cutitem = new JMenuItem("Cut");
cutitem.setAccelerator(KeyStroke.getKeyStroke('X', InputEvent.CTRL_DOWN_MASK));
copyitem = new JMenuItem("Copy Text");
pasteitem = new JMenuItem("Paste Text");
deleteitem = new JMenuItem("Delete (Del)");
finditem = new JMenuItem("Find Text/Word (Ctrl + F)");
findnextitem = new JMenuItem("Find NextItem(F3)");
replaceitem = new JMenuItem("Replace A Piece Of Text (Ctrl + H)");
gotoitem = new JMenuItem("Goto... (Ctrl + G)");
selectallitem = new JMenuItem("Select All (Ctrl + A)");
timeanddateitem = new JMenuItem("Time & Date (F5)");
wordwrapitem = new JMenuItem("WordWrap Item...");
fontitem = new JMenuItem("Color ");
statusbaritem = new JMenuItem("Status Bar");
viewhelpitem = new JMenuItem("View Help");
aboutnotepaditem = new JMenuItem("About Notepad");
filemenu.add(newitem);
filemenu.add(openitem);
filemenu.add(saveitem);
filemenu.add(saveasitem);
filemenu.addSeparator();
filemenu.add(pagesetupitem);
filemenu.add(printitem);
filemenu.addSeparator();
filemenu.add(exititem);
editmenu.add(undoitem);
filemenu.addSeparator();
editmenu.add(cutitem);
editmenu.add(copyitem);
editmenu.add(pasteitem);
editmenu.add(deleteitem);
editmenu.addSeparator();
editmenu.add(finditem);
editmenu.add(findnextitem);
editmenu.add(replaceitem);
editmenu.add(gotoitem);
editmenu.addSeparator();
editmenu.add(selectallitem);
editmenu.add(timeanddateitem);
formatmenu.add(wordwrapitem);
formatmenu.add(fontitem);
viewmenu.add(statusbaritem);
helpmenu.add(viewhelpitem);
helpmenu.add(aboutnotepaditem);
// SETTING THE TITLE/MAKING THE WINDOW
setTitle("Untitled -- SwiftPad");
setVisible(true);
setExtendedState(MAXIMIZED_BOTH);
newitem.addActionListener(this);
openitem.addActionListener(this);
saveitem.addActionListener(this);
saveasitem.addActionListener(this);
exititem.addActionListener(this);
copyitem.addActionListener(this);
cutitem.addActionListener(this);
pasteitem.addActionListener(this);
fontitem.addActionListener(this);
}
public void actionPerformed(ActionEvent ae) {
if (ae.getSource() == exititem) {
System.exit(0);
}
if (ae.getSource() == newitem) {
ta.setText("");
}
if (ae.getSource() == copyitem) {
ta.copy();
}
if (ae.getSource() == pasteitem) {
ta.paste();
}
if (ae.getSource() == cutitem) {
ta.cut();
}
if (ae.getSource() == openitem) {
String s = ta.getText();
if (!(s.equalsIgnoreCase(""))) {
int opt = JOptionPane.showConfirmDialog(this, " Unsaved Documents! Do you want to save them? y/n? :)");
if (opt == JOptionPane.YES_OPTION) {
jfc.showOpenDialog(this);
try {
FileWriter fw = new FileWriter(jfc.getSelectedFile());
String data = ta.getText();
fw.write(data + "\n");
fw.close();
} catch (Exception e) {
JOptionPane.showMessageDialog(this, "Error in Reading :(", "Error", JOptionPane.ERROR_MESSAGE);
}
}
} else {
jfc.showOpenDialog(this);
try {
FileReader fr = new FileReader(jfc.getSelectedFile());
BufferedReader br = new BufferedReader(fr);
String data = "";
ta.setText("");
while ((data = br.readLine()) != null) {
ta.append(data + "\n");
}
fr.close();
} catch (Exception e) {
JOptionPane.showMessageDialog(this, "Error In Opening :(", "Error", JOptionPane.ERROR_MESSAGE);
}
}
}
if(ae.getSource() == saveitem) {
jfc.showSaveDialog(this);
try {
FileWriter fw = new FileWriter(jfc.getSelectedFile());
String data = ta.getText();
fw.write(data + "\n");
fw.close();
}catch (Exception e) {
JOptionPane.showMessageDialog(this, "Error In Saving :(");
}
}
}
// RUNNING CLASS
public static void main(String[] args) {
new Notepad();
}
}
這是我得到的錯誤，我用java製作了遊戲，但是得到了它一次，但從來沒有，請幫助！ :)
Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Unknown Source)
at java.awt.Container.add(Unknown Source)
at javax.swing.JMenuBar.add(Unknown Source)
at com.anmol.notepad.Notepad.<init>(Notepad.java:79)
at com.anmol.notepad.Notepad.main(Notepad.java:221)
謝謝，Anmol！
可能重複[什麼是空指針異常，以及如何解決它？]（http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how -do-i-fix-it） –
請在代碼示例中標記第79行。 –
@Simz我看了一下這個帖子之前，我做了這個我沒有得到它 –