您好，我正在制作一个项目，该项目从文件中读取书籍列表，我想添加在按下按钮时添加新书的可能性。但我收到很多错误。看我的代码:
public class Biblioteka {
public static void main(String[] args) {
JFrame frame = new JFrame("Biblioteka");
frame.setVisible(true);
frame.setSize(400, 400);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new JPanel();
frame.add(panel);
GridBagConstraints c = new GridBagConstraints();
JButton button = new JButton("Print List");
JButton button2 = new JButton("Add book");
c.gridx = 0;
c.gridy = 0;
c.insets = new Insets(10, 10, 10, 10);
panel.add(button);
panel.add(button2);
final List<Book> listofbooks = new ArrayList<>();
try {
File file = new File("newfile.txt");
Scanner input = new Scanner(file);
while (input.hasNextLine()) {
String input1 = input.nextLine();// read one line
String num[] = input1.split("\\|");// split line by "|"
int howMuch = Integer.parseInt(num[2]);
Book k1 = new Book(num[0], num[1], howMuch);
listofbooks.add(k1);
}
} catch (FileNotFoundException nf) {
System.err.format("File does not exist");
}
final JLabel labelis = new JLabel();
for (Book book : listofbooks) {
labelis.setText("<html> "
+ labelis.getText()
+ "<br> Name: " + book.getName()
+ " Tile: " + book.getTitle()
+ " Number of books: "
+ book.getHowMany()
);
}
labelis.setText(labelis.getText() + "</html>");
button.addActionListener(new Action() {
@Override
public void actionPerformed(ActionEvent e) {
JFrame frame2 = new JFrame("Clicked");
frame2.setVisible(true);
frame2.setSize(400, 300);
JPanel panelis = new JPanel();
panelis.add(labelis);
frame2.add(panelis);
}
});
当我想添加一本新书时，程序崩溃了:
button2.addActionListener(new Action() {
@Override
public void actionPerformed(ActionEvent e) {
String knygAutorius = JOptionPane.showInputDialog("Input author: ");
String knygPav = JOptionPane.showInputDialog("Input title: ");
int knygKiek = Integer.parseInt(JOptionPane.showInputDialog("How many books do you want to add: "));
int i = 0;
for (Book book : listofbooks) {
if ((book.getTitle().equals(knygPav)) && (book.getName().equals(knygAutorius))) {
int kiekis = book.getHowMany();
kiekis = kiekis + knygKiek;
Book k2 = new Book(knygAutorius, knygPav, kiekis);
listofbooks.set(i, k2);
} else {
Book nauja = new Book(knygAutorius, knygPav, knygKiek);
listofbooks.add(nauja);
}
i++;
}
}
});
}
static class Action implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
}
}
}
我有一本书:
public class Book {
String name;
String bookTitle;
int howMany;
public Book(String name, String bookTitle, int howMany) {
this.name = name;
this.bookTitle = bookTitle;
this.howMany = howMany;
}
public String getName() {
return this.name;
}
public String getTitle() {
return this.bookTitle;
}
public int getHowMany() {
return this.howMany;
}
}
您可以尝试编译我的代码并查看问题。也许你可以帮助我。 错误:
Exception in thread "AWT-EventQueue-0" java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:859)
at java.util.ArrayList$Itr.next(ArrayList.java:831)
at biblioteka.Biblioteka$2.actionPerformed(Biblioteka.java:83)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$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.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3320)
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)
最佳答案
明白了，为什么您收到上述错误是您正在向该列表添加一本新书，并再次在 for 循环中调用同一列表，因此您会收到
**java.util.ConcurrentModificationException**
import java.awt.GridBagConstraints;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
public class Biblioteka {
public static void main(String[] args) {
JFrame frame = new JFrame("Biblioteka");
frame.setVisible(true);
frame.setSize(400, 400);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new JPanel();
frame.add(panel);
GridBagConstraints c = new GridBagConstraints();
JButton button = new JButton("Print List");
JButton button2 = new JButton("Add book");
c.gridx = 0;
c.gridy = 0;
c.insets = new Insets(10, 10, 10, 10);
panel.add(button);
panel.add(button2);
final List<Book> listofbooks = new ArrayList<Book>();
try {
File file = new File("d:\\a.txt");
Scanner input = new Scanner(file);
while (input.hasNextLine()) {
String input1 = input.nextLine();// read one line
String num[] = input1.split(" ");// split line by "|"
int howMuch = Integer.parseInt(num[2]);
client.Book k1 = new client.Book(num[0], num[1], howMuch);
listofbooks.add(k1);
}
} catch (FileNotFoundException nf) {
System.err.format("File does not exist");
}
final JLabel labelis = new JLabel();
button.addActionListener(new Action() {
@Override
public void actionPerformed(ActionEvent e) {
JFrame frame2 = new JFrame("Clicked");
frame2.setVisible(true);
frame2.setSize(400, 300);
JPanel panelis = new JPanel();
panelis.add(labelis);
//Moving for loop inside,so latest update on the books will be printed
//This is the reason you are not getting the modified count before
for (Book book : listofbooks) {
labelis.setText("<html> "
+ labelis.getText()
+ "<br> Name: " + book.getName()
+ " Tile: " + book.getTitle()
+ " Number of books: "
+ book.getHowMany()
);
}
labelis.setText(labelis.getText() + "</html>");
frame2.add(panelis);
}
});
button2.addActionListener(new Action() {
@Override
public void actionPerformed(ActionEvent e) {
String knygAutorius = JOptionPane.showInputDialog("Input author: ");
String knygPav = JOptionPane.showInputDialog("Input title: ");
int knygKiek = Integer.parseInt(JOptionPane.showInputDialog("How many books do you want to add: "));
int i = 0;
for (Book book : listofbooks) {
if ((book.getTitle().equals(knygPav)) && (book.getName().equals(knygAutorius))) {
int kiekis = book.getHowMany();
kiekis = kiekis + knygKiek;
book.setHowMany(kiekis);
break;
}
i++;
}
if(listofbooks.size()==i){
Book nauja = new Book(knygAutorius, knygPav, knygKiek);
listofbooks.add(nauja);
}
}
});
}
static class Action implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
}
}
}
对 Book.java 进行小修改以设置书籍数量
public class Book {
String name;
String bookTitle;
int howMany;
public Book(String name, String bookTitle, int howMany) {
this.name = name;
this.bookTitle = bookTitle;
this.howMany = howMany;
}
public String getName() {
return this.name;
}
public String getTitle() {
return this.bookTitle;
}
public int getHowMany() {
return this.howMany;
}
//to set the total books
public void setHowMany(int total){
howMany=total;
}
}
关于java - 使用javax.swing输入信息并将其存储在Array List中，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22515814/