为什么这个选择下拉框不跳转其他日历JPanel panel2 = new JPanel（）;panel2.setLayout（new GridLayout（7，7））;7*7的网格 panel2.add（new JLabel（“一”，SwingConstants.CENTER））;panel2.add（new JLabel（“二”，SwingConstants.CENTER））;panel2.add（new JLabel（“三”，SwingConstants.CENTER））;panel2.add（new JLabel（“四”，SwingConstants.CENTER））;panel2.add（new JLabel（“五”，SwingConstants.CENTER））;panel2.add（new JLabel（“六”，SwingConstants.CENTER））;panel2.add（new JLabel（“日”，SwingConstants.CENTER））;int year = comboBoxYear.getSelectedIndex（）;int month = comboBoxMonth.getSelectedIndex（）;日历第一个月份的一天 = 日历.getInstance（）;firstDayOfMonth.set（year，month-1，1）;int firstDayOfWeek = firstDayOfMonth.get（Calendar.DAY_OF_WEEK）-1;int numOfMonth = firstDayOfMonth.getActualMaximum（Calendar.DAY_OF_MONTH）;整数 k，num = 1;字符串编号;for（k = 0;k < 42;k++）{ if（k < firstDayOfWeek - 2||k >= firstDayOfWeek + numOfMonth-2）{ panel2.add（new JLabel（“”，SwingConstants.CENTER））; }else{ number = String.valueOf（num）; panel2.add（new JLabel（number，SwingConstants.CENTER））; num++; } }ActionListener listener = e -> { int year1 = comboBoxYear.getSelectedIndex（）; int month1 = comboBoxMonth.getSelectedIndex（）;Calendar firstDayOfMonth1 = Calendar.getInstance（）;首日1.集（年1，月1-1，1）;int firstDayOfWeek1 = firstDayOfMonth1.get（Calendar.DAY_OF_WEEK）-1;int numOfMonth1 = firstDayOfMonth1.getActualMaximum（Calendar.DAY_OF_MONTH）;整数 k1， 数字 1 = 1;字符串编号 1;for（k1 = 0; k1 < 42; k1++）{ if（k1 < firstDayOfWeek1 - 2|| k1 >= firstDayOfWeek1 + numOfMonth1 -2）{ panel2.add（new JLabel（“”，SwingConstants.CENTER））; }else{ number1 = String.valueOf（num1）; panel2.add（new JLabel（number1，SwingConstants.CENTER））; num1++; } }};comboBoxYear.addActionListener（listener）;comboBoxMonth.addActionListener（listener）;

可能是因为你没有将这个选择下拉框与其他日历JPanel进行关联。你需要在监听器中添加代码来更新其他日历JPanel的显示内容。具体来说，当选择下拉框的值发生变化时，你需要重新计算该月份的第一天是星期几以及该月份有多少天，然后更新其他日历JPanel的显示内容。你可以通过遍历JPanel中的所有标签来实现更新。

相关问题

javaGUI通过下拉框选择日期来显示日历，不要额外加按钮

可以使用JComboBox来创建下拉框，然后根据选择的日期更新日历显示。

下面是一个简单的实现，可以根据需要进行修改和优化：

import java.awt.*;
import java.awt.event.*;
import java.time.*;
import java.time.format.*;
import javax.swing.*;

public class CalendarGUI extends JFrame implements ActionListener {
    private final JComboBox<String> yearBox, monthBox;
    private final JLabel[] dayLabels;
    private final DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("yyyy-M-d");
    
    public CalendarGUI() {
        setTitle("Calendar");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());
        
        JPanel topPanel = new JPanel();
        topPanel.add(new JLabel("Year:"));
        yearBox = new JComboBox<>();
        for (int year = LocalDate.now().getYear() - 10; year <= LocalDate.now().getYear() + 10; year++) {
            yearBox.addItem(String.valueOf(year));
        }
        yearBox.setSelectedItem(String.valueOf(LocalDate.now().getYear()));
        yearBox.addActionListener(this);
        topPanel.add(yearBox);
        topPanel.add(new JLabel("Month:"));
        monthBox = new JComboBox<>();
        for (int month = 1; month <= 12; month++) {
            monthBox.addItem(String.valueOf(month));
        }
        monthBox.setSelectedItem(String.valueOf(LocalDate.now().getMonthValue()));
        monthBox.addActionListener(this);
        topPanel.add(monthBox);
        add(topPanel, BorderLayout.NORTH);
        
        JPanel centerPanel = new JPanel(new GridLayout(7, 7));
        String[] weekDays = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
        for (String weekDay : weekDays) {
            centerPanel.add(new JLabel(weekDay, SwingConstants.CENTER));
        }
        dayLabels = new JLabel[42];
        for (int i = 0; i < dayLabels.length; i++) {
            dayLabels[i] = new JLabel("", SwingConstants.CENTER);
            centerPanel.add(dayLabels[i]);
        }
        updateCalendar();
        add(centerPanel, BorderLayout.CENTER);
        
        pack();
        setLocationRelativeTo(null);
        setVisible(true);
    }
    
    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == yearBox || e.getSource() == monthBox) {
            updateCalendar();
        }
    }
    
    private void updateCalendar() {
        int year = Integer.parseInt((String) yearBox.getSelectedItem());
        int month = Integer.parseInt((String) monthBox.getSelectedItem());
        LocalDate date = LocalDate.of(year, month, 1);
        int firstDayOfWeek = date.getDayOfWeek().getValue() % 7;
        int lastDay = date.plusMonths(1).minusDays(1).getDayOfMonth();
        for (int i = 0; i < dayLabels.length; i++) {
            if (i < firstDayOfWeek || i >= firstDayOfWeek + lastDay) {
                dayLabels[i].setText("");
            } else {
                dayLabels[i].setText(String.valueOf(i - firstDayOfWeek + 1));
            }
        }
    }
    
    public static void main(String[] args) {
        SwingUtilities.invokeLater(CalendarGUI::new);
    }
}

这个GUI界面包含一个顶部面板和一个中心面板。顶部面板包含两个下拉框，用于选择年份和月份；中心面板包含一个网格布局，用于显示日历。网格布局中第一行为星期几的标签，接下来是42个用于显示日期的标签（最多有6*7=42天）。当用户选择年份或月份时，通过计算更新中心面板中的日期标签。

javaGUI显示日历小程序，不用字符串，使用下拉框，通过选择下拉框的年，月显示对应的当月日历，没有额外按钮，只通过选择下拉框显示日历，使用Calendar类

好的，这是一个简单的Java GUI日历小程序，使用了下拉框和Calendar类来显示当月日历。

import java.awt.*;
import java.awt.event.*;
import java.util.Calendar;
import javax.swing.*;

public class CalendarGUI extends JFrame implements ItemListener {
    private static final long serialVersionUID = 1L;

    private JComboBox<String> yearComboBox;
    private JComboBox<String> monthComboBox;
    private JLabel[] dayLabels;
    private JPanel calendarPanel;

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            new CalendarGUI().setVisible(true);
        });
    }

    public CalendarGUI() {
        setTitle("Calendar");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(400, 300);
        setLocationRelativeTo(null);

        Container contentPane = getContentPane();
        contentPane.setLayout(new BorderLayout());

        JPanel controlPanel = new JPanel();
        controlPanel.setLayout(new FlowLayout());

        yearComboBox = new JComboBox<>();
        yearComboBox.addItemListener(this);
        for (int i = 1900; i <= 2100; i++) {
            yearComboBox.addItem(String.valueOf(i));
        }
        controlPanel.add(yearComboBox);

        monthComboBox = new JComboBox<>();
        monthComboBox.addItemListener(this);
        for (int i = 1; i <= 12; i++) {
            monthComboBox.addItem(String.valueOf(i));
        }
        controlPanel.add(monthComboBox);

        contentPane.add(controlPanel, BorderLayout.NORTH);

        calendarPanel = new JPanel();
        calendarPanel.setLayout(new GridLayout(0, 7));

        String[] dayNames = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
        dayLabels = new JLabel[7];
        for (int i = 0; i < 7; i++) {
            dayLabels[i] = new JLabel(dayNames[i], JLabel.CENTER);
            dayLabels[i].setForeground(Color.BLUE);
            calendarPanel.add(dayLabels[i]);
        }

        contentPane.add(calendarPanel, BorderLayout.CENTER);

        Calendar calendar = Calendar.getInstance();
        int year = calendar.get(Calendar.YEAR);
        int month = calendar.get(Calendar.MONTH) + 1;
        yearComboBox.setSelectedItem(String.valueOf(year));
        monthComboBox.setSelectedItem(String.valueOf(month));
        updateCalendar(year, month);
    }

    private void updateCalendar(int year, int month) {
        Calendar calendar = Calendar.getInstance();
        calendar.set(year, month - 1, 1);

        int firstDayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);
        int lastDayOfMonth = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);

        calendarPanel.removeAll();

        for (int i = 1; i < firstDayOfWeek; i++) {
            calendarPanel.add(new JLabel(""));
        }

        for (int i = 1; i <= lastDayOfMonth; i++) {
            JLabel dayLabel = new JLabel(String.valueOf(i), JLabel.CENTER);
            if (i == calendar.get(Calendar.DAY_OF_MONTH)) {
                dayLabel.setForeground(Color.RED);
            }
            calendarPanel.add(dayLabel);
        }

        pack();
    }

    @Override
    public void itemStateChanged(ItemEvent e) {
        if (e.getStateChange() == ItemEvent.SELECTED) {
            int year = Integer.parseInt((String) yearComboBox.getSelectedItem());
            int month = Integer.parseInt((String) monthComboBox.getSelectedItem());
            updateCalendar(year, month);
        }
    }
}

在这个程序中，我们首先创建了一个窗口和两个下拉框，其中一个用于选择年份，另一个用于选择月份。当用户选择年份或月份时，我们将调用`updateCalendar`方法来显示相应的日历。`updateCalendar`方法将使用Calendar类来计算该月份的第一天是星期几，以及该月份有多少天。然后，我们将创建一个网格布局，将星期几标签和日期标签添加到其中。如果当前日期与选定日期相同，我们将以红色显示该日期。最后，我们使用`pack`方法调整窗口大小以适应内容。