我不确定我做错了什么，但我的JPanels的文字没有显示出来。我只是得到问题编号文本，但问题没有显示出来。我有什么想法吗？
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
class NewFrame extends JFrame {
JPanel centerpanel; // For the questions.
CardLayout card; // For the centerpanel.
JTextField tf; // Used in question 1.
boolean // Store selections for Q2.
q2Option1,
q2Option2,
q2Option3,
q2Option4;
JList q4List; // For question 4.
double // Score on each question.
q1Score = 0,
q2Score = 0,
q3Score = 0,
q4Score = 0;
// Constructor.
public NewFrame (int width, int height)
{
this.setTitle ("Snoot Club Membership Test");
this.setResizable (true);
this.setSize (width, height);
Container cPane = this.getContentPane();
// cPane.setLayout (new BorderLayout());
// First, a welcome message, as a Label.
JLabel L = new JLabel ("<html><b>Are you elitist enough for our exclusive club?"
+ " <br>Fill out the form and find out</b></html>");
L.setForeground (Color.blue);
cPane.add (L, BorderLayout.NORTH);
// Now the center panel with the questions.
card = new CardLayout ();
centerpanel = new JPanel ();
centerpanel.setLayout (card);
centerpanel.setOpaque (false);
// Each question will be created in a separate method.
// The cardlayout requires a label as second parameter.
centerpanel.add (firstQuestion (), "1");
centerpanel.add (secondQuestion(), "2");
centerpanel.add (thirdQuestion(), "3");
centerpanel.add (fourthQuestion(), "4");
cPane.add (centerpanel, BorderLayout.CENTER);
// Next, a panel of four buttons at the bottom.
// The four buttons: quit, submit, next-question, previous-question.
JPanel bottomPanel = getBottomPanel ();
cPane.add (bottomPanel, BorderLayout.SOUTH);
// Finally, show the frame.
this.setVisible (true);
}
// No-parameter constructor.
public NewFrame ()
{
this (500, 300);
}
// The first question uses labels for the question and
// gets input via a textfield. A panel containing all
// these things is returned. The question asks for
// a vacation destination: the more exotic the location,
// the higher the score.
JPanel firstQuestion ()
{
// We will package everything into a panel and return the panel.
JPanel subpanel = new JPanel ();
// We will place things in a single column, so
// a GridLayout with one column is appropriate.
subpanel.setLayout (new GridLayout (8,1));
JLabel L1 = new JLabel ("Question 1:");
L1.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L1);
JLabel L2 = new JLabel (" Select a vacation destination");
L2.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L2);
JLabel L3 = new JLabel (" 1. Baltimore");
L3.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L3);
JLabel L4 = new JLabel (" 2. Disneyland");
L4.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L4);
JLabel L5 = new JLabel (" 3. Grand Canyon");
L5.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L5);
JLabel L6 = new JLabel (" 4. French Riviera");
L6.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L6);
JLabel L7 = new JLabel ("Enter 1,2,3 or 4 below:");
L7.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L7);
// Here's the textfield to get user-input.
tf = new JTextField ();
tf.addActionListener (
new ActionListener () {
// This interface has only one method.
public void actionPerformed (ActionEvent a)
{
String q1String = a.getActionCommand();
if (q1String.equals ("2"))
q1Score = 2;
else if (q1String.equals ("3"))
q1Score = 3;
else if (q1String.equals ("4"))
q1Score = 4;
else
q1Score = 1;
}
}
);
subpanel.add (tf);
return subpanel;
}
// For the second question, a collection of checkboxes
// will be used. More than one selection can be made.
// A listener is required for each checkbox. The state
// of each checkbox is recorded.
JPanel secondQuestion ()
{
JPanel subpanel = new JPanel ();
subpanel.setLayout (new GridLayout (7,1));
JLabel L1 = new JLabel ("Question 2:");
L1.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L1);
JLabel L2 = new JLabel (" Select ONE OR MORE things that ");
L2.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L2);
JLabel L3 = new JLabel (" you put into your lunch sandwich");
L3.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L3);
// Initialize the selections to false.
q2Option1 = q2Option2 = q2Option3 = q2Option4 = false;
// First checkbox.
JCheckBox c1 = new JCheckBox ("Ham, beef or turkey");
c1.addItemListener (
new ItemListener () {
public void itemStateChanged (ItemEvent i)
{
JCheckBox c = (JCheckBox) i.getSource();
q2Option1 = c.isSelected();
}
}
);
subpanel.add (c1);
// Second checkbox.
JCheckBox c2 = new JCheckBox ("Cheese");
c2.addItemListener (
new ItemListener () {
// This is where we will react to a change in checkbox.
public void itemStateChanged (ItemEvent i)
{
JCheckBox c = (JCheckBox) i.getSource();
q2Option2 = c.isSelected();
}
}
);
subpanel.add (c2);
// Third checkbox.
JCheckBox c3 = new JCheckBox ("Sun-dried Arugula leaves");
c3.addItemListener (
new ItemListener () {
public void itemStateChanged (ItemEvent i)
{
JCheckBox c = (JCheckBox) i.getSource();
q2Option3 = c.isSelected();
}
}
);
subpanel.add (c3);
// Fourth checkbox.
JCheckBox c4 = new JCheckBox ("Lemon-enhanced smoked Siberian caviar");
c4.addItemListener (
new ItemListener () {
public void itemStateChanged (ItemEvent i)
{
JCheckBox c = (JCheckBox) i.getSource();
q2Option4 = c.isSelected();
}
}
);
subpanel.add (c4);
return subpanel;
}
// The third question allows only one among four choices
// to be selected. We will use radio buttons.
JPanel thirdQuestion ()
{
JPanel subpanel = new JPanel ();
subpanel.setLayout (new GridLayout (6,1));
JLabel L1 = new JLabel ("Question 3:");
L1.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L1);
JLabel L2 = new JLabel (" And which mustard do you use?");
L2.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L2);
// First, create the ButtonGroup instance.
// We will add radio buttons to this group.
ButtonGroup bGroup = new ButtonGroup();
// First checkbox.
JRadioButton r1 = new JRadioButton ("Who cares?");
r1.addItemListener (
new ItemListener () {
public void itemStateChanged (ItemEvent i)
{
JRadioButton r = (JRadioButton) i.getSource();
if (r.isSelected()) q3Score = 1;
}
}
);
bGroup.add (r1);
subpanel.add (r1);
// Second checkbox.
JRadioButton r2 = new JRadioButton ("Safeway Brand");
r2.addItemListener (
new ItemListener () {
public void itemStateChanged (ItemEvent i)
{
JRadioButton r = (JRadioButton) i.getSource();
if (r.isSelected()) q3Score = 2;
}
}
);
bGroup.add (r2);
subpanel.add (r2);
// Third checkbox.
JRadioButton r3 = new JRadioButton ("Fleishman's");
r3.addItemListener (
new ItemListener () {
public void itemStateChanged (ItemEvent i)
{
JRadioButton r = (JRadioButton) i.getSource();
if (r.isSelected()) q3Score = 3;
}
}
);
bGroup.add (r3);
subpanel.add (r3);
// Fourth checkbox.
JRadioButton r4 = new JRadioButton ("Grey Poupon");
r4.addItemListener (
new ItemListener () {
public void itemStateChanged (ItemEvent i)
{
JRadioButton r = (JRadioButton) i.getSource();
if (r.isSelected()) q3Score = 4;
}
}
);
bGroup.add (r4);
subpanel.add (r4);
return subpanel;
}
// For the fourth question we will use a drop-down Choice.
JPanel fourthQuestion ()
{
JPanel subpanel = new JPanel ();
subpanel.setLayout (new GridLayout (3,1));
JLabel L1 = new JLabel ("Question 4:");
L1.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L1);
JLabel L2 = new JLabel (" Your movie preference, among these:");
L2.setFont (new Font ("SansSerif", Font.ITALIC, 15));
subpanel.add (L2);
// Create a JList with options.
String[] movies = { "Lethal Weapon IV", "Titanic", "Saving Private Ryan",
"Le Art Movie avec subtitles"};
q4List = new JList (movies);
q4Score = 1;
q4List.addListSelectionListener (
new ListSelectionListener () {
public void valueChanged (ListSelectionEvent e)
{
q4Score = 1 + q4List.getSelectedIndex();
}
}
);
subpanel.add (q4List);
return subpanel;
}
void computeResult ()
{
// Clear the center panel.
centerpanel.removeAll();
// Create a new panel to display in the center.
JPanel subpanel = new JPanel (new GridLayout (5,1));
// Score on question 1.
JLabel L1 = new JLabel ("Score on question 1: " + q1Score);
L1.setFont (new Font ("Serif", Font.ITALIC, 15));
subpanel.add (L1);
// Score on question 2.
if (q2Option1) q2Score += 1;
if (q2Option2) q2Score += 2;
if (q2Option3) q2Score += 3;
if (q2Option4) q2Score += 4;
q2Score = 0.6 * q2Score;
JLabel L2 = new JLabel ("Score on question 2: " + q2Score);
L2.setFont (new Font ("Serif", Font.ITALIC, 15));
subpanel.add (L2);
// Score on question 3.
JLabel L3 = new JLabel ("Score on question 3: " + q3Score);
L3.setFont (new Font ("Serif", Font.ITALIC, 15));
subpanel.add (L3);
// Score on question 4.
JLabel L4 = new JLabel ("Score on question 4: " + q4Score);
L4.setFont (new Font ("Serif", Font.ITALIC, 15));
subpanel.add (L4);
// Weighted score.
double avg = (q1Score + q2Score + q3Score + q4Score) / (double) 4;
JLabel L5;
if (avg <= 3.5)
L5 = new JLabel ("Your average score: " + avg + " - REJECTED!");
else
L5 = new JLabel ("Your average score: " + avg + " - WELCOME!");
L5.setFont (new Font ("Serif", Font.BOLD, 20));
//L5.setAlignment (JLabel.CENTER);
subpanel.add (L5);
// Now add the new subpanel.
centerpanel.add (subpanel, "5");
// Need to mark the centerpanel as "altered"
centerpanel.invalidate();
// Everything "invalid" (e.g., the centerpanel above)
// is now re-computed.
this.validate();
}
JPanel getBottomPanel ()
{
// Create a panel into which we will place buttons.
JPanel bottomPanel = new JPanel ();
// A "previous-question" button.
JButton backward = new JButton ("Previous question");
backward.setFont (new Font ("Serif", Font.PLAIN | Font.BOLD, 15));
backward.addActionListener (
new ActionListener () {
public void actionPerformed (ActionEvent a)
{
// Go back in the card layout.
card.previous (centerpanel);
}
}
);
bottomPanel.add (backward);
// A forward button.
JButton forward = new JButton ("Next question");
forward.setFont (new Font ("Serif", Font.PLAIN | Font.BOLD, 15));
forward.addActionListener (
new ActionListener () {
public void actionPerformed (ActionEvent a)
{
// Go forward in the card layout.
card.next (centerpanel);
}
}
);
bottomPanel.add (forward);
// A submit button.
JButton submit = new JButton ("Submit");
submit.setFont (new Font ("Serif", Font.PLAIN | Font.BOLD, 15));
submit.addActionListener (
new ActionListener () {
public void actionPerformed (ActionEvent a)
{
// Perform submit task.
computeResult();
}
}
);
bottomPanel.add (submit);
JButton quitb = new JButton ("Quit");
quitb.setFont (new Font ("Serif", Font.PLAIN | Font.BOLD, 15));
quitb.addActionListener (
new ActionListener () {
public void actionPerformed (ActionEvent a)
{
System.exit (0);
}
}
);
bottomPanel.add (quitb);
return bottomPanel;
}
}
public class Survey {
public static void main (String[] argv)
{
NewFrame nf = new NewFrame (600, 300);
}
}
答案 0 :(得分：2)
我刚尝试过它似乎有用 - 您使用的是哪个版本的Java，以及在什么平台上使用？
BTW：当你说
new GridLayout(8,1)
它实际上做的是创建一个总是有8行的GridLayout。如果你向它添加另一个项目，它实际上会创建一个新列（GridLayout只关心你传递它的第一个非零参数）。
你的意思是：
new GridLayout(0, 1);
答案 1 :(得分：1)
我在代码中看到的两件事：
CardLayout。您应该使用addLayoutComponent(Component, Object)添加它们，使用String作为您将用于显示面板的第二个参数。要显示您的面板，您应该使用使用CardLayout作为第一个arg的面板调用show(Container, String)方法。main主题中完成所有工作。您应该在EventDispatchThread中完成所有GUI绘制工作。 See this link关于Swing中线程的概念。