Question

下午好。我已经创建了一个入门java课程的应用程序，允许用户按标题，工作室或年份对他们的DVD集合进行排序。该应用程序还允许用户将其他DVD添加到其集合中，从而扩大其阵列。代码正确编译，但由于标题，工作室和年份混合在一起，显然有一些错误。需要说明的是，此代码来自教科书，是实验室的一部分，需要使用您在代码中看到的确切方法，包等。我不是在寻求有关如何提高代码效率的建议（虽然这在我学习时很受欢迎），但具体而言导致“争夺”的代码有什么问题。这是我的代码：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;

public class DVD extends JFrame implements ActionListener
{
    // construct components
    JLabel sortPrompt = new JLabel("Sort by:");
    JComboBox fieldCombo = new JComboBox();
    JTextPane textPane = new JTextPane();

    // initialize data in arrays
    String title[] = {"Casablanca", "Citizen Kane", "Singin' in the Rain", "The Wizard of Oz"};
    String studio[] = {"Warner Brothers", "RKO Pictures", "MGM", "MGM"};
    String year[] = {"1942", "1941", "1952", "1939"};

    // construct instance of DVD
    public DVD()
    {
        super("Classics on DVD");
    }

    // create the menu system
    public JMenuBar createMenuBar()
    {
        // create an instance of the menu
        JMenuBar mnuBar = new JMenuBar();
        setJMenuBar(mnuBar);

        // construct and populate the File menu
        JMenu mnuFile = new JMenu("File", true);
            mnuFile.setMnemonic(KeyEvent.VK_F);
            mnuFile.setDisplayedMnemonicIndex(0);
            mnuBar.add(mnuFile);

        JMenuItem mnuFileExit = new JMenu("Exit");
            mnuFileExit.setMnemonic(KeyEvent.VK_X);
            mnuFileExit.setDisplayedMnemonicIndex(1);
            mnuFile.add(mnuFileExit);
            mnuFileExit.setActionCommand("Exit");
            mnuFileExit.addActionListener(this);

        // contruct and populate the Edit menu
        JMenu mnuEdit = new JMenu("Edit", true);
            mnuEdit.setMnemonic(KeyEvent.VK_E);
            mnuEdit.setDisplayedMnemonicIndex(0);
            mnuBar.add(mnuEdit);

        JMenuItem mnuEditInsert = new JMenuItem("Insert New DVD");
            mnuEditInsert.setMnemonic(KeyEvent.VK_I);
            mnuEditInsert.setDisplayedMnemonicIndex(0);
            mnuEdit.add(mnuEditInsert);
            mnuEditInsert.setActionCommand("Insert");
            mnuEditInsert.addActionListener(this);

        JMenu mnuEditSearch = new JMenu("Search");
            mnuEditSearch.setMnemonic(KeyEvent.VK_R);
            mnuEditSearch.setDisplayedMnemonicIndex(3);
            mnuEdit.add(mnuEditSearch);

        JMenuItem mnuEditSearchByTitle = new JMenuItem("by Title");
            mnuEditSearchByTitle.setMnemonic(KeyEvent.VK_T);
            mnuEditSearchByTitle.setDisplayedMnemonicIndex(3);
            mnuEditSearch.add(mnuEditSearchByTitle);
            mnuEditSearchByTitle.setActionCommand("title");
            mnuEditSearchByTitle.addActionListener(this);

        JMenuItem mnuEditSearchByStudio = new JMenuItem("by Studio");
            mnuEditSearchByStudio.setMnemonic(KeyEvent.VK_S);
            mnuEditSearchByStudio.setDisplayedMnemonicIndex(3);
            mnuEditSearch.add(mnuEditSearchByStudio);
            mnuEditSearchByStudio.setActionCommand("studio");
            mnuEditSearchByStudio.addActionListener(this);

        JMenuItem mnuEditSearchByYear = new JMenuItem("by Year");
            mnuEditSearchByYear.setMnemonic(KeyEvent.VK_Y);
            mnuEditSearchByYear.setDisplayedMnemonicIndex(3);
            mnuEditSearch.add(mnuEditSearchByYear);
            mnuEditSearchByYear.setActionCommand("year");
            mnuEditSearchByYear.addActionListener(this);

        return mnuBar;
    }

    // create the content pane
    public Container createContentPane()
    {
        // populate the JComboBox
        fieldCombo.addItem("Title");
        fieldCombo.addItem("Studio");
        fieldCombo.addItem("Year");
        fieldCombo.addActionListener(this);
        fieldCombo.setToolTipText("Click the drop-down arrow to display sort fields.");

        // construct and populate the north panel
        JPanel northPanel = new JPanel();
            northPanel.setLayout(new FlowLayout());
            northPanel.add(sortPrompt);
            northPanel.add(fieldCombo);

        // create the JTextPane and center panel
        JPanel centerPanel = new JPanel();
            setTabsAndStyles(textPane);
            textPane = addTextToTextPane();
            JScrollPane scrollPane = new JScrollPane(textPane);
                scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
                scrollPane.setPreferredSize(new Dimension(500, 200));
            centerPanel.add(scrollPane);

        // create Container and set attributes
        Container c = getContentPane();
            c.setLayout(new BorderLayout(10,10));
            c.add(northPanel,BorderLayout.NORTH);
            c.add(centerPanel,BorderLayout.CENTER);

        return c;
    }

    // method to create tab stops and set font styles
    protected void setTabsAndStyles(JTextPane textPane)
    {
        // create Tab Stops
        TabStop[] tabs = new TabStop[2];
            tabs[0] = new TabStop(200, TabStop.ALIGN_LEFT, TabStop.LEAD_NONE);
            tabs[1] = new TabStop(350, TabStop.ALIGN_LEFT, TabStop.LEAD_NONE);
        TabSet tabset = new TabSet(tabs);

        // set Tab Style
        StyleContext tabStyle = StyleContext.getDefaultStyleContext();
        AttributeSet aset =
            tabStyle.addAttribute(SimpleAttributeSet.EMPTY, StyleConstants.TabSet, tabset);
        textPane.setParagraphAttributes(aset, false);

        // set Font styles
        Style fontStyle =
            StyleContext.getDefaultStyleContext().getStyle(StyleContext.DEFAULT_STYLE);

        Style regular = textPane.addStyle("regular", fontStyle);
        StyleConstants.setFontFamily(fontStyle, "SansSerif");

        Style s = textPane.addStyle("italic", regular);
        StyleConstants.setItalic(s, true);

        s = textPane.addStyle("bold", regular);
        StyleConstants.setBold(s, true);

        s = textPane.addStyle("large", regular);
        StyleConstants.setFontSize(s, 16);
    }

    // method to add new text to the JTextPane
    public JTextPane addTextToTextPane()
    {
        Document doc = textPane.getDocument();
        try
        {
            // clear the previous text
            doc.remove(0, doc.getLength());

            // insert title
            doc.insertString(0,"TITLE\tSTUDIO\tYEAR\n",textPane.getStyle("large"));

            // insert detail
            for (int j = 0; j<title.length; j++)
            {
                doc.insertString(doc.getLength(), title[j] + "\t", textPane.getStyle("bold"));
                doc.insertString(doc.getLength(), studio[j] + "\t", textPane.getStyle("italic"));
                doc.insertString(doc.getLength(), year[j] + "\t", textPane.getStyle("regular"));
            }
        }
        catch(BadLocationException ble)
        {
            System.err.println("Couldn't insert text.");
        }

        return textPane;
    }

    // event to process user clicks
    public void actionPerformed(ActionEvent e)
    {
        String arg = e.getActionCommand();

        // user clicks the sort by combo box
        if (e.getSource() == fieldCombo)
        {
            switch(fieldCombo.getSelectedIndex())
            {
                case 0:
                    sort(title);
                    break;
                case 1:
                    sort(studio);
                    break;
                case 2:
                    sort(year);
                    break;
            }
        }

        // user clicks Exit on the File menu
        if (arg == "Exit")
            System.exit(0);

        // user clicks Insert New DVD on the Edit Menu
        if (arg == "Insert")
        {
            // accept new data
            String newTitle = JOptionPane.showInputDialog(null, "Please enter the new movie's title");
            String newStudio = JOptionPane.showInputDialog(null, "Please enter the studio for " + newTitle);
            String newYear = JOptionPane.showInputDialog(null, "Please enter the year for " + newTitle);

            // enlarge arrays
            title = enlargeArray(title);
            studio = enlargeArray(studio);
            year = enlargeArray(year);

            // add new data to arrays
            title[title.length-1] = newTitle;
            studio[studio.length-1] = newStudio;
            year[year.length-1] = newYear;

            // call sort method
            sort(title);
            fieldCombo.setSelectedIndex(0);
        }

        // user clicks Title on the Search submenu
        if (arg == "title")
            search(arg, title);

        // user clicks Studio on the Search submenu
        if (arg == "studio")
            search(arg, studio);

        // user clicks Year on the Search submenu
        if (arg == "year")
            search(arg, year);
    }

    // method to enlarge an array by 1
    public String[] enlargeArray(String[] currentArray)
    {
        String[] newArray = new String[currentArray.length + 1];
        for (int i = 0; i<currentArray.length; i++)
            newArray[i] = currentArray[i];
        return newArray;
    }

    // method to sort arrays
    public void sort(String tempArray[])
    {
        // loop ton control number of passes
        for (int pass = 1; pass < tempArray.length; pass++)
        {
            for (int element = 0; element < tempArray.length - 1; element++)
                if (tempArray[element].compareTo(tempArray[element + 1])>0)
                {
                    swap(title, element, element + 1);
                    swap(studio, element, element + 1);
                    swap(year, element, element + 1);
                }
        }
        addTextToTextPane();
    }

    // method to swap two elements of an array
    public void swap(String swapArray[], int first, int second)
    {
        String hold; // temporary holding area for swap
        hold = swapArray[first];
        swapArray[first] = swapArray[second];
        swapArray[second] = hold;
    }

    public void search(String searchField, String searchArray[])
    {
        try
        {
            Document doc = textPane.getDocument(); // assign text to document object
            doc.remove(0,doc.getLength()); // clear previous text

            // display column titles
            doc.insertString(0,"TITLE\tSTUDIO\tYEAR\n",textPane.getStyle("large"));

            // prompt user for search data
            String search = JOptionPane.showInputDialog(null, "Please enter the "+searchField);
            boolean found = false;

            // search arrays
            for (int i = 0; i<title.length; i++)
            {
                if (search.compareTo(searchArray[i])==0)
                {
                    doc.insertString(doc.getLength(), title[i] + "\t", textPane.getStyle("bold"));
                    doc.insertString(doc.getLength(), studio[i] + "\t", textPane.getStyle("italic"));
                    doc.insertString(doc.getLength(), year[i] + "\t", textPane.getStyle("regular"));
                    found = true;
                }
            }
            if (found == false)
            {
                JOptionPane.showMessageDialog(null, "Your search produced no results.","No results found",JOptionPane.INFORMATION_MESSAGE);
                sort(title);
            }
        }
        catch(BadLocationException ble)
        {
            System.err.println("Couldn't insert text.");
        }
    }

    // main method executes at run time
    public static void main(String arg[])
    {
        JFrame.setDefaultLookAndFeelDecorated(true);
        DVD f = new DVD();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setJMenuBar(f.createMenuBar());
        f.setContentPane(f.createContentPane());
        f.setSize(600,375);
        f.setVisible(true);
    }
}

这是一个屏幕截图，让您了解我的意思是“混乱”。 Scrambled Application

显然，所有的标题都应该在标题栏，工作室的工作室和年份中。

与往常一样，我很欣赏这一指导。

Answer 1

问题在于这一行

doc.insertString(doc.getLength(), year[j] + "\t", textPane.getStyle("regular"));

您在年份之后放置了一个标签（"\t"），但您需要一个换行符（"\n"）。这条线就变成了

doc.insertString(doc.getLength(), year[j] + "\n", textPane.getStyle("regular"));

Answer 2

在将DVD的年份添加到文档后，您是否只是错过了换行符？即。

doc.insertString(doc.getLength(), year[j] + "\n", textPane.getStyle("regular"));

数组排序不正确

2 个答案: