我的 JCheckBox 程序只显示一个框。这是为什么？
My JCheckBox program only displays one box. Why is that?
我正在尝试向该程序添加另一个复选框，但由于某些原因，当我 运行 该程序时它不会显示。仅显示蓝色药丸的复选框。我试图添加一些东西或改变程序的结构方式，但到目前为止我所做的一切都没有帮助。
代码如下：
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class CMIS242WK4DonnersonAReply {
static JCheckBox red;
static JCheckBox blue;
static JButton button;
public CMIS242WK4DonnersonAReply() {
button = new JButton("submit"); // Creates submit button
widget
ButtonHandler listener = new ButtonHandler(); // Creates the handler for the button.
button.addActionListener((ActionListener) listener); // adds the handler to the button widget
JPanel content = new JPanel(); // "container"
content.setLayout(new BorderLayout());
content.add(button, BorderLayout.PAGE_END);// places submit button at the bottom of panel.
JLabel label = new JLabel("At last. Welcome, Neo. As you no doubt have guessed, I am Morpheus. This is your last chance. After this there is no turning back."); // Label in frame.
content.add(label, BorderLayout.NORTH);// places label at the top of the screen.
//Creating Check Boxes
JCheckBox red = new JCheckBox("You take the red pill, you stay in Wonderland and I show you how deep the rabbit hole goes.");
red.setBounds(100,100, 50,50);
content.add(red);
JCheckBox blue = new JCheckBox("You take the blue pill, the story ends, you wake up in your bed and believe whatever you want to believe. ");
blue.setBounds(100,100, 50,50);
content.add(blue);
//Adding Frame
JFrame window = new JFrame("Matrix Monologue"); // JFrame = Window
window.setContentPane(content);
window.setSize(750,200); // Length, Height
window.setLocation(200,200); // X/Y "OF THE ENTIRE FRAME" Not the contents
window.setVisible(true); // makes window visible
}
// Method handles what happens when button is pressed.
private static class ButtonHandler implements ActionListener{
public void actionPerformed1(ActionEvent e) {
// Checks if which pill was selected and responds to user depending on their action.
if (red.isSelected() == true) {
System.out.println("Follow me");
System.out.println();
}
if (blue.isSelected() == true) {
System.out.println("Very Well, You may go back to your world");
System.out.println();
}
else
System.out.println("You must make a choice for what pill you will take");
System.exit(0); //closes program
}
@Override
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
}
}
// Main/driver method that runs everything.
public static void main(String[] args) {
CMIS242WK4DonnersonAReply matrixMonologue= new CMIS242WK4DonnersonAReply();
}
}
有什么指点吗？
当您遇到问题时，返回并参考 documentation。
您会找到这样的信息：
A border layout lays out a container, arranging and resizing its
components to fit in five regions: north, south, east, west, and
center. Each region may contain no more than one component, and is
identified by a corresponding constant: NORTH, SOUTH, EAST, WEST, and
CENTER. When adding a component to a container with a border layout,
use one of these five constants...
当你添加你的按钮时，你这样做：
content.add(button, BorderLayout.PAGE_END);
但是，当需要添加复选框时，您可以这样做：
content.add(red);
...
content.add(blue);
你看到少了什么了吗？我敢打赌，您只会看到蓝色复选框，因为您将其添加到（或只是替换）了红色复选框之上。请记住，文档说“每个区域最多只能包含一个组件...”
尝试指定要在 BorderLayout 中看到每个复选框的区域。
如果您希望它们出现在同一区域，请将它们放在它们自己的 JPanel 中并将它们布置在 NORTH 和 SOUTH 或 EAST 和 WEST，然后将该复选框面板添加到您的 content 面板在您希望它们出现的区域。
我觉得您的 Swing 编程需要一些指导。我已经重写了你的 CMIS242WK4DonnersonAReply class。代码如下。但首先要对您问题中的代码发表一些评论。
JCheckBox red = new JCheckBox("You take the red pill, you stay in Wonderland and I show you how deep the rabbit hole goes.");
您已经创建了一个局部变量，它是 hiding class 成员。因此 static JCheckBox red; 保持为空，因此下面的 if 语句将抛出 NullPointerException.
if (red.isSelected() == true) {
顺便说一下，== true 不是必需的。以下就够了。
if (red.isSelected()) {
现在还有一点。
red.setBounds(100,100, 50,50);
由于您使用的是 layout manager，即 BorderLayout，方法 setBounds 将被忽略。布局管理器决定组件在屏幕上的位置。
window.setContentPane(content);
默认情况下，JFrame 的内容窗格是 JPanel 和 BorderLayout，因此无需替换默认内容窗格。
private static class ButtonHandler implements ActionListener
无需创建嵌套 class。只需让 class CMIS242WK4DonnersonAReply 实现 ActionListener 接口。
System.out.println("Follow me");
我认为将控制台包含在 GUI 应用程序中不是一个好主意。我会使用 JOptionPane 向用户显示消息。
static JCheckBox blue;
我认为 JRadioButton 比 JCheckBox 更适合你的情况。
这是我的代码。
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BoxLayout;
import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
public class CMIS242WK4DonnersonAReply implements Runnable, ActionListener {
private JButton button;
private JRadioButton blue;
private JRadioButton red;
private JFrame window;
@Override
public void actionPerformed(ActionEvent event) {
if (red.isSelected()) {
JOptionPane.showMessageDialog(window, "Follow me.");
}
else if (blue.isSelected()) {
JOptionPane.showMessageDialog(window, "Very Well, You may go back to your world");
}
else {
JOptionPane.showMessageDialog(window, "You must make a choice for what pill you will take");
}
}
@Override
public void run() {
createAndShowGui();
}
private void createAndShowGui() {
window = new JFrame("Matrix Monologue");
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel label = new JLabel("At last. Welcome, Neo. As you no doubt have guessed, I am Morpheus. This is your last chance. After this there is no turning back."); // Label in frame.
window.add(label, BorderLayout.PAGE_START);
window.add(createCheckBoxes(), BorderLayout.CENTER);
JPanel buttonPanel = new JPanel();
button = new JButton("submit");
button.addActionListener(this);
buttonPanel.add(button);
window.add(buttonPanel, BorderLayout.PAGE_END);
window.setSize(750,200); // Length, Height
window.setLocation(200,200); // X/Y "OF THE ENTIRE FRAME" Not the contents
window.setVisible(true); // makes window visible
}
private JPanel createCheckBoxes() {
JPanel panel = new JPanel();
BoxLayout layout = new BoxLayout(panel, BoxLayout.PAGE_AXIS);
panel.setLayout(layout);
red = new JRadioButton("You take the red pill, you stay in Wonderland and I show you how deep the rabbit hole goes.");
blue = new JRadioButton("You take the blue pill, the story ends, you wake up in your bed and believe whatever you want to believe.");
ButtonGroup grp = new ButtonGroup();
grp.add(red);
grp.add(blue);
panel.add(red);
panel.add(blue);
return panel;
}
public static void main(String[] args) {
EventQueue.invokeLater(new CMIS242WK4DonnersonAReply());
}
}
这是我 运行 应用程序的外观。
我正在尝试向该程序添加另一个复选框，但由于某些原因，当我 运行 该程序时它不会显示。仅显示蓝色药丸的复选框。我试图添加一些东西或改变程序的结构方式，但到目前为止我所做的一切都没有帮助。
代码如下：
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
public class CMIS242WK4DonnersonAReply {
static JCheckBox red;
static JCheckBox blue;
static JButton button;
public CMIS242WK4DonnersonAReply() {
button = new JButton("submit"); // Creates submit button
widget
ButtonHandler listener = new ButtonHandler(); // Creates the handler for the button.
button.addActionListener((ActionListener) listener); // adds the handler to the button widget
JPanel content = new JPanel(); // "container"
content.setLayout(new BorderLayout());
content.add(button, BorderLayout.PAGE_END);// places submit button at the bottom of panel.
JLabel label = new JLabel("At last. Welcome, Neo. As you no doubt have guessed, I am Morpheus. This is your last chance. After this there is no turning back."); // Label in frame.
content.add(label, BorderLayout.NORTH);// places label at the top of the screen.
//Creating Check Boxes
JCheckBox red = new JCheckBox("You take the red pill, you stay in Wonderland and I show you how deep the rabbit hole goes.");
red.setBounds(100,100, 50,50);
content.add(red);
JCheckBox blue = new JCheckBox("You take the blue pill, the story ends, you wake up in your bed and believe whatever you want to believe. ");
blue.setBounds(100,100, 50,50);
content.add(blue);
//Adding Frame
JFrame window = new JFrame("Matrix Monologue"); // JFrame = Window
window.setContentPane(content);
window.setSize(750,200); // Length, Height
window.setLocation(200,200); // X/Y "OF THE ENTIRE FRAME" Not the contents
window.setVisible(true); // makes window visible
}
// Method handles what happens when button is pressed.
private static class ButtonHandler implements ActionListener{
public void actionPerformed1(ActionEvent e) {
// Checks if which pill was selected and responds to user depending on their action.
if (red.isSelected() == true) {
System.out.println("Follow me");
System.out.println();
}
if (blue.isSelected() == true) {
System.out.println("Very Well, You may go back to your world");
System.out.println();
}
else
System.out.println("You must make a choice for what pill you will take");
System.exit(0); //closes program
}
@Override
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
}
}
// Main/driver method that runs everything.
public static void main(String[] args) {
CMIS242WK4DonnersonAReply matrixMonologue= new CMIS242WK4DonnersonAReply();
}
}
有什么指点吗？
当您遇到问题时，返回并参考 documentation。
您会找到这样的信息：
A border layout lays out a container, arranging and resizing its components to fit in five regions: north, south, east, west, and center. Each region may contain no more than one component, and is identified by a corresponding constant: NORTH, SOUTH, EAST, WEST, and CENTER. When adding a component to a container with a border layout, use one of these five constants...
当你添加你的按钮时，你这样做：
content.add(button, BorderLayout.PAGE_END);
但是，当需要添加复选框时，您可以这样做：
content.add(red);
...
content.add(blue);
你看到少了什么了吗？我敢打赌，您只会看到蓝色复选框，因为您将其添加到（或只是替换）了红色复选框之上。请记住，文档说“每个区域最多只能包含一个组件...”
尝试指定要在 BorderLayout 中看到每个复选框的区域。
如果您希望它们出现在同一区域，请将它们放在它们自己的 JPanel 中并将它们布置在 NORTH 和 SOUTH 或 EAST 和 WEST，然后将该复选框面板添加到您的 content 面板在您希望它们出现的区域。
我觉得您的 Swing 编程需要一些指导。我已经重写了你的 CMIS242WK4DonnersonAReply class。代码如下。但首先要对您问题中的代码发表一些评论。
JCheckBox red = new JCheckBox("You take the red pill, you stay in Wonderland and I show you how deep the rabbit hole goes.");
您已经创建了一个局部变量，它是 hiding class 成员。因此 static JCheckBox red; 保持为空，因此下面的 if 语句将抛出 NullPointerException.
if (red.isSelected() == true) {
顺便说一下，== true 不是必需的。以下就够了。
if (red.isSelected()) {
现在还有一点。
red.setBounds(100,100, 50,50);
由于您使用的是 layout manager，即 BorderLayout，方法 setBounds 将被忽略。布局管理器决定组件在屏幕上的位置。
window.setContentPane(content);
默认情况下，JFrame 的内容窗格是 JPanel 和 BorderLayout，因此无需替换默认内容窗格。
private static class ButtonHandler implements ActionListener
无需创建嵌套 class。只需让 class CMIS242WK4DonnersonAReply 实现 ActionListener 接口。
System.out.println("Follow me");
我认为将控制台包含在 GUI 应用程序中不是一个好主意。我会使用 JOptionPane 向用户显示消息。
static JCheckBox blue;
我认为 JRadioButton 比 JCheckBox 更适合你的情况。
这是我的代码。
import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BoxLayout;
import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
public class CMIS242WK4DonnersonAReply implements Runnable, ActionListener {
private JButton button;
private JRadioButton blue;
private JRadioButton red;
private JFrame window;
@Override
public void actionPerformed(ActionEvent event) {
if (red.isSelected()) {
JOptionPane.showMessageDialog(window, "Follow me.");
}
else if (blue.isSelected()) {
JOptionPane.showMessageDialog(window, "Very Well, You may go back to your world");
}
else {
JOptionPane.showMessageDialog(window, "You must make a choice for what pill you will take");
}
}
@Override
public void run() {
createAndShowGui();
}
private void createAndShowGui() {
window = new JFrame("Matrix Monologue");
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JLabel label = new JLabel("At last. Welcome, Neo. As you no doubt have guessed, I am Morpheus. This is your last chance. After this there is no turning back."); // Label in frame.
window.add(label, BorderLayout.PAGE_START);
window.add(createCheckBoxes(), BorderLayout.CENTER);
JPanel buttonPanel = new JPanel();
button = new JButton("submit");
button.addActionListener(this);
buttonPanel.add(button);
window.add(buttonPanel, BorderLayout.PAGE_END);
window.setSize(750,200); // Length, Height
window.setLocation(200,200); // X/Y "OF THE ENTIRE FRAME" Not the contents
window.setVisible(true); // makes window visible
}
private JPanel createCheckBoxes() {
JPanel panel = new JPanel();
BoxLayout layout = new BoxLayout(panel, BoxLayout.PAGE_AXIS);
panel.setLayout(layout);
red = new JRadioButton("You take the red pill, you stay in Wonderland and I show you how deep the rabbit hole goes.");
blue = new JRadioButton("You take the blue pill, the story ends, you wake up in your bed and believe whatever you want to believe.");
ButtonGroup grp = new ButtonGroup();
grp.add(red);
grp.add(blue);
panel.add(red);
panel.add(blue);
return panel;
}
public static void main(String[] args) {
EventQueue.invokeLater(new CMIS242WK4DonnersonAReply());
}
}
这是我 运行 应用程序的外观。