[英]My text does not change. I don't understand why
我不明白為什么這個Java代碼無法正常工作。 這是我正在處理的一個GUI項目,並且我試圖通過一些復選框將JLabel更改為粗體,斜體等:
import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ButtonGroup;
import javax.swing.JCheckBox;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
public class FontViewer {
static JCheckBox checkBoxBold;
static JCheckBox checkBoxItalic;
static JCheckBox checkBoxCenter;
static JPanel textPanel;
static JLabel textLabel;
static JComboBox fontName;
static JComboBox fontSize;
static ActionListener listener;
public static void main(String[] args) {
final int FRAME_SIZE_X = 250;
final int FRAME_SIZE_Y = 400;
JFrame frame = new JFrame();
frame.setSize(FRAME_SIZE_X, FRAME_SIZE_Y);
JPanel face = new JPanel();
face.setLayout(new GridLayout(2, 1));
JPanel bottomFace = new JPanel();
bottomFace.setLayout(new GridLayout(3, 1));
textPanel = createTextPanel();
JPanel checkBoxPanel = createCheckBoxPanel();
JPanel comboPanel = createComboPanel();
JPanel radioButtonsPanel = createButtonsPanel();
face.add(textPanel);
bottomFace.add(checkBoxPanel);
bottomFace.add(comboPanel);
bottomFace.add(radioButtonsPanel);
face.add(bottomFace);
frame.add(face);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
class FontListener implements ActionListener {
public void actionPerformed(ActionEvent event) {
int fontStyle = 0;
if (checkBoxBold.isSelected())
fontStyle = fontStyle + Font.BOLD;
if (checkBoxItalic.isSelected())
fontStyle = fontStyle + Font.ITALIC;
if (checkBoxCenter.isSelected())
textPanel.add(textLabel, BorderLayout.CENTER);
String textFont = (String) fontName.getSelectedItem();
int textSize = Integer.parseInt((String) fontSize
.getSelectedItem());
textLabel.setFont(new Font(textFont, fontStyle, textSize));
textLabel.repaint();
}
}
listener = new FontListener();
}
private static JPanel createTextPanel() {
textPanel = new JPanel();
textPanel.setLayout(new BorderLayout());
textLabel = new JLabel("Java Text");
textPanel.add(textLabel, BorderLayout.WEST);
return textPanel;
}
private static JPanel createCheckBoxPanel() {
JPanel checkBoxPanel = new JPanel();
checkBoxBold = new JCheckBox("Bold");
checkBoxItalic = new JCheckBox("Italic");
checkBoxCenter = new JCheckBox("Center");
checkBoxBold.addActionListener(listener);
checkBoxItalic.addActionListener(listener);
checkBoxCenter.addActionListener(listener);
checkBoxPanel.add(checkBoxBold);
checkBoxPanel.add(checkBoxItalic);
checkBoxPanel.add(checkBoxCenter);
return checkBoxPanel;
}
private static JPanel createComboPanel() {
JPanel comboPanel = new JPanel();
fontName = new JComboBox();
fontName.addItem("Serif");
fontName.addItem("Courier");
fontSize = new JComboBox();
fontSize.addItem("12");
fontSize.addItem("24");
fontSize.addItem("36");
comboPanel.add(fontName);
comboPanel.add(fontSize);
return comboPanel;
}
private static JPanel createButtonsPanel() {
JPanel radioButtonsPanel = new JPanel();
JRadioButton redButton = new JRadioButton("Red");
JRadioButton whiteButton = new JRadioButton("White");
JRadioButton blueButton = new JRadioButton("Blue");
ButtonGroup colors = new ButtonGroup();
colors.add(redButton);
colors.add(whiteButton);
colors.add(blueButton);
radioButtonsPanel.add(redButton);
radioButtonsPanel.add(whiteButton);
radioButtonsPanel.add(blueButton);
return radioButtonsPanel;
}
}
當我按下任何一個復選框時,JLabel對象都不會更改。 非常感謝您的幫助,在此先感謝您。
注意:到目前為止,我只想知道為什么復選框不起作用。 這段代碼不完整,我知道這一點。 再一次感謝你。
在將偵聽器添加到復選框時, listener
的值為null
。 直到main方法的最后,才初始化listener
器。
創建JFrame
之前,請嘗試初始化偵聽器。 它為我工作。 當然,必須將FontListener
類的定義相應地放在listener
聲明之前。
//...
listener = new FontListener();
JFrame frame = new JFrame();
//...
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