一切都显示并且工作正常，但每当我加载它时菜单都不会显示。我在这做错了什么？我试着尝试其他的东西，以使它工作，但它永远不会。有什么建议吗？
Java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 Bros.", "RKO Pictures", "MGM", "MGM"};
String year[] = {"1942", "1941", "1952", "1939"};
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(1);
mnuFile.add(mnuFile);
// construct and populate the Exit menu
JMenuItem mnuFileExit = new JMenuItem("Exit");
mnuFileExit.setMnemonic(KeyEvent.VK_X);
mnuFileExit.setDisplayedMnemonicIndex(1);
mnuFile.add(mnuFileExit);
mnuFileExit.setActionCommand("Exit");
mnuFileExit.addActionListener(this);
// construct and populate the Edit menu
JMenu mnuEdit = new JMenu("Edit", true);
mnuEdit.setMnemonic(KeyEvent.VK_E);
mnuEdit.setDisplayedMnemonicIndex(0);
mnuEdit.add(mnuEdit);
// Insert
JMenuItem mnuEditInsert = new JMenuItem("Insert new DVD");
mnuEditInsert.setMnemonic(KeyEvent.VK_I);
mnuEditInsert.setDisplayedMnemonicIndex(0);
mnuEdit.add(mnuEditInsert);
mnuEditInsert.setActionCommand("Insert");
mnuEditInsert.addActionListener(this);
// Search
JMenu mnuEditSearch = new JMenu("Search", true);
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()
{
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);
textPane.setEditable(false);
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 style
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 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] + "\n", 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(); // execute the getActionCommand() (java method) store in arg
//user clicks the sort by Combo box // combo field is one of the selections in an array format
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 necessary for search
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 and 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 to 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] + "\n", 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 args[])
{
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);
}
}
答案 0 :(得分：1)
您必须将其添加到菜单栏才能使用它。
mnuBar.add(mnuFile);
这条线似乎是罪魁祸首：
mnuFile.add(mnuFile);