Java 试图让GUI从一开始就循环处理数据

我试图让GUI完全循环 但在第三次单击“下一步”按钮后，我遇到了一个错误[2]。我需要做的是在单击“下一步”按钮时让整个过程循环进行。一旦到达数组的最后一次迭代，就需要返回到开始。还有一点是数组是按字母顺序排序的，所以循环之后需要以标题[3]开头。谢谢你的帮助

import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.*;
import java.util.Arrays;
import javax.swing.*;
import java.awt.*;



public class GUI extends JFrame implements ActionListener {
    JButton next;
    JButton previous;
    JButton first;
    JButton last;

    private JLabel itmNum = new JLabel("Item Number: ", SwingConstants.RIGHT);
    private JTextField itemNumber;
    private JLabel proNm = new JLabel ("Product Name: ", SwingConstants.RIGHT);
    private JTextField prodName;
    private JLabel yr = new JLabel("Year Made: ", SwingConstants.RIGHT);
    private JTextField year;
    private JLabel unNum = new JLabel("Unit Number: ", SwingConstants.RIGHT);
    private JTextField unitNumber;
    private JLabel prodPrice = new JLabel("Product Price: ", SwingConstants.RIGHT);
    private JTextField price;
    private JLabel restkFee = new JLabel("Restocking Fee", SwingConstants.RIGHT);
    private JTextField rsFee;
    private JLabel prodInValue = new JLabel("Product Inventory Value", SwingConstants.RIGHT);
    private JTextField prodValue;
    private JLabel totalValue = new JLabel("Total Value of All Products", SwingConstants.RIGHT);
    private JTextField tValue;
    private double toValue;
    Movies[] titles = new Movies[9];
    int nb = 0;

    public GUI() 
    {

        super ("Inventory Program Part 5");
        setSize(800,800);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLookAndFeel();




        first = new JButton("First");
        previous = new JButton("Previous");
        next = new JButton("Next");
        last = new JButton("Last");
        first.addActionListener(this);
        previous.addActionListener(this);
        next.addActionListener(this);
        last.addActionListener(this);




        //Movies[] titles = new Movies[9];

        titles [0] = new Movies(10001, "King Arthur", 25 , 9.99, 2004, .05);

        titles [1] = new Movies(10002,"Tron", 25, 7.99, 1982, .05);

        titles [2] = new Movies(10003, "Tron: Legacy",25,24.99,2010,.05);

        titles [3] = new Movies(10004,"Braveheart", 25,2.50,1995,.05);

        titles [4] = new Movies(10005,"Gladiator",25,2.50,2000,.05);

        titles [5] = new Movies(10006,"CaddyShack SE",25,19.99,1980,.05);

        titles [6] = new Movies (10007,"Hackers",25,12.50,1995,.05);

        titles [7] = new Movies (10008,"Die Hard Trilogy",25,19.99,1988,.05);

        titles [8] = new Movies (10009,"Terminator",25,4.99,1984,.05);

        Arrays.sort (titles, DVD.prodNameComparator);






                        itemNumber = new JTextField(Double.toString(titles[3].getitemNum()));
                        prodName = new JTextField(titles[3].getprodName());
                        year= new JTextField(Integer.toString(titles[3].getYear()));
                        unitNumber= new JTextField(Integer.toString(titles[3].getunitNum()));
                        price= new JTextField(Float.toString(titles[3].getprice()));
                        rsFee= new JTextField(Double.toString(titles[3].getRestkFee()));
                        prodValue= new JTextField(Double.toString(titles[3].getprodValue()));
                        tValue= new JTextField("2636");
                        nb=0;
                        next.addActionListener(this);



        setLayout(new GridLayout(8,4));
        add(itmNum);
        add(itemNumber);
        add(proNm);
        add(prodName);
        add(yr);
        add(year);
        add(unNum);
        add(unitNumber);
        add(prodPrice);
        add(price);
        add(restkFee);
        add(rsFee);
        add(prodInValue);
        add(prodValue);
        add(totalValue);
        add(tValue);
        add(first);
        add(previous);
        add(next);
        add(last);
        setLookAndFeel();
        setVisible(true);


    }



    public void updateFields()
    {
        nb++;
        itemNumber.setText(Double.toString(titles[nb].getitemNum()));
        prodName.setText(titles[nb].getprodName());
        year.setText(Integer.toString(titles[nb].getYear()));
        unitNumber.setText(Integer.toString(titles[nb].getunitNum()));
        price.setText(Double.toString(titles[nb].getprice()));
        rsFee.setText(Double.toString(titles[nb].getRestkFee()));
        prodValue.setText(Double.toString(titles[nb].getprodValue()));

    }




    public void actionPerformed(ActionEvent evt){
        Object source = evt.getSource();
        if (source == next) 
        {
            if (titles[nb]== titles[8])
            {
                titles[nb] = titles[0];
            }
            else {
                nb++;
            }
            updateFields();
        }

    }

    private void setLookAndFeel()
    {
        try{
            UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
                        SwingUtilities.updateComponentTreeUI(this);
            } catch (Exception e) {
                System.err.println("couln't use the system"+ "look and feel: " + e);
            }

    }


    }

---

您在记录中前进如此之快的原因是您已将

ActionListener

添加到

next

JButton

两次：

这反过来会增加

ActionListener

以及

updateFields

方法中的记录索引（

nb

）。从其中一个位置删除此增量

此外，当您检查是否已到达最后一个标题时，您从未重置记录索引

nb

。你可以做：

if (titles[nb] == titles[8]) {
   nb = 0;
   ...

---

我看到并删除了它，但一旦我点击标题[2]程序崩溃，我发现另一件有趣的事情是它应该从标题[3]开始，但它从标题[4]开始，所以我从元素0开始，第一个显示的是标题[3]这是应该的，因为它是按字母顺序排序的，但它跳过了其他元素。我知道你在说什么，谢谢你的帮助。现在我注意到，当我尝试添加“下一步”按钮时，我会遇到一些问题。

if (titles[nb] == titles[8]) {
   nb = 0;
   ...