Question

我正在开发一个我正在创建GUI翻书的项目。我想要做的是在文本区域放置一些文本。然后去一个干净的幻灯片。加入更多文字。我保存了所有＆＃34;幻灯片＆＃34;在数组列表中。我在GUI上有按钮，允许用户在幻灯片之间来回切换。当我点击＆＃34;之前的＆＃34;我遇到了一个错误。按钮。我在线程＆＃39; AWT-EventQueue-0＆＃39;中得到了一个＆＃34;异常。 java.util.ConcurrentModficationException＆＃34;在那之下有更多的错误。

这段代码仍处于严谨的构建状态，因此其中一些有点粗糙。类的名称有点奇怪 - 我正在修改教科书中的GUI程序版本。

import javax.swing.*;
import java.awt.event.*;  
import java.awt.*;
//import java.util.Scanner;
import java.util.*;
import java.io.*;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;


public class MetricConverter extends JFrame {
    private JPanel panel; //To reference a panel
    private JLabel messageLabel; //To reference a label
    private JTextArea kiloTextField; //To refrence a text field - this will become the JtextArea
    private JButton Previous;
    private JButton Menu;
    private JButton Load;
    private JButton Save;
    private JButton Next;
    private final int WINDOW_WIDTH = 400;
    private final int WINDOW_HEIGHT = 400;

    LinkedList ll = new LinkedList();//Created Linked List
    ArrayList al = new ArrayList();//Create an array list
    Iterator itr = al.iterator();
    ListIterator litr = al.listIterator();  


    public MetricConverter()
    {
        setTitle("Java Flipbook");

        setSize(WINDOW_WIDTH, WINDOW_HEIGHT);

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        buildPanel();//Build the panel and add it to the frame

        add(panel);//Add the panel to the frame's content pane

        setVisible(true);//Display the window

    }
    /* The build panel label method adds a label, a text field, and a button to a panel    */         
    private void buildPanel()
    {   //create the buttons
        messageLabel = new JLabel("Make a flipbook!");    
        kiloTextField = new JTextArea(10,15);//Create the canvas             
        //Create a button for the Previous Slide
        Previous = new JButton("Previous");
        Previous.addActionListener(new PrevButton());
        //Create a button to bring up the menu
        Menu = new JButton("Menu");
        Load = new JButton("Load");
        Save = new JButton("Save");
        //Create a button for the Next Slide
        Next = new JButton("Next");
        Next.addActionListener(new Next());        
        //Create a JPanel object and let the panel field reference it
        panel = new JPanel();        
        //Add the label, text field, and button components to the panel.
        //panel.add(messageLabel);
        panel.add(kiloTextField);
        panel.add(Previous);
        // panel.add(Menu);
        panel.add(Load);
        panel.add(Save);
        panel.add(Next);       
    } //end buildPanel class


    private class Next implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            String s = kiloTextField.getText();
            al.add(s);//add to array list
            //ll.add(s);//add whatever is in the JtextArea to the linked list
            kiloTextField.setText(null);//"clear" the canvas
        }
    } 

    private class PrevButton implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            String s = kiloTextField.getText();//
            //Object element = litr.previous();
            //System.out.print(element);
            //System.out.print(ll);
            System.out.println(litr.previous());
        }
    }         
    // Main Method          
    public static void main(String[] args)
    {
        new MetricConverter();
    }
}

Answer 1

要启用它，您需要在类中声明一个Integer变量（如全局），以跟踪光标的位置。这将使您能够移动到前一个和前一个，直到第一个。

public class MetricConverter extends JFrame {

    private JPanel panel; //To reference a panel
    private JLabel messageLabel; //To reference a label
    private JTextArea kiloTextField; //To refrence a text field - this will become the JtextArea
    private JButton Previous;
    private JButton Menu;
    private JButton Load;
    private JButton Save;
    private JButton Next;
    private final int WINDOW_WIDTH = 400;
    private final int WINDOW_HEIGHT = 400;

    LinkedList ll = new LinkedList();//Created Linked List
    ArrayList al = new ArrayList();//Create an array list
    Iterator itr = al.iterator();
    ListIterator litr = al.listIterator();
    int previousIndex = 0; //<====================================Changes made here

    public MetricConverter() {
         //no changes were made here
    }

    /* The build panel label method adds a label, a text field, and a button to a panel    */
    private void buildPanel() {   //create the buttons
        //no changes were made here
    } //end buildPanel class

    private class Next implements ActionListener {

        public void actionPerformed(ActionEvent e) {
            String s = kiloTextField.getText();
            al.add(s);//add to array list
            litr = al.listIterator(); //<====================================Changes made here
            //ll.add(s);//add whatever is in the JtextArea to the linked list
            kiloTextField.setText(null);//"clear" the canvas

            //navigates to the last Object in the list
            while (litr.hasNext()) { //<====================================Changes made here
                litr.next();
            }
            //keeps track of where the cursor is
            previousIndex = litr.previousIndex();//<====================================Changes made here
        }
    }

    private class PrevButton implements ActionListener {

        public void actionPerformed(ActionEvent e) {
            String s = kiloTextField.getText();//
            //Object element = litr.previous();
            //System.out.print(element);
            //System.out.print(ll);
            //System.out.println("arr : "+al.toString());

            if (previousIndex > -1) { //<====================================Changes made here
                litr = al.listIterator(previousIndex+1);//sets the cursor to the previous object's index

                System.out.println(litr.previous());

                previousIndex--;
            }

        }
    }

    // Main Method          
    public static void main(String[] args) {
        new MetricConverter();
    }
}

注意我在哪里进行了更改。

Answer 2

发生错误是因为您有一个迭代器，但是在创建它之后直接修改它的列表。您只应在迭代后通过迭代器修改列表。

一般来说，将Iterator作为一个类的成员是没有意义的。你需要重新考虑这一切。

尝试迭代数组列表时，线程中的Java GUI异常

2 个答案: