要用Java写一个带有窗体的日历，可以使用Java的Swing库来创建窗体和组件。
下面是一个简单的示例代码，展示了如何使用Java编写一个带有窗体的日历：
import javax.swing.*;import java.awt.*;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import java.time.LocalDate;import java.time.YearMonth;public class CalendarApp extends JFrame { private YearMonth currentYearMonth; private JLabel monthLabel; private JButton prevButton; private JButton nextButton; private JTable calendarTable; public CalendarApp() { currentYearMonth = YearMonth.now(); setTitle("Calendar App"); setSize(400, 300); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); setLocationRelativeTo(null); monthLabel = new JLabel("", JLabel.CENTER); calendarTable = new JTable(6, 7); prevButton = new JButton("Prev"); prevButton.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { currentYearMonth = currentYearMonth.minusMonths(1); updateCalendar(); } }); nextButton = new JButton("Next"); nextButton.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { currentYearMonth = currentYearMonth.plusMonths(1); updateCalendar(); } }); updateCalendar(); setLayout(new BorderLayout()); add(monthLabel, BorderLayout.NORTH); add(new JScrollPane(calendarTable), BorderLayout.CENTER); JPanel buttonPanel = new JPanel(); buttonPanel.add(prevButton); buttonPanel.add(nextButton); add(buttonPanel, BorderLayout.SOUTH); } private void updateCalendar() { monthLabel.setText(currentYearMonth.getYear() + "年" + currentYearMonth.getMonthValue() + "月"); LocalDate firstDayOfMonth = currentYearMonth.atDay(1); int firstDayOfWeek = firstDayOfMonth.getDayOfWeek().getValue(); int daysInMonth = currentYearMonth.lengthOfMonth(); int numRows = (int) Math.ceil((firstDayOfWeek + daysInMonth) / 7.0); String[] columnNames = {"周日", "周一", "周二", "周三", "周四", "周五", "周六"}; Object[][] data = new Object[numRows][7]; int day = 1 - firstDayOfWeek; for (int i = 0; i < numRows; i++) { for (int j = 0; j < 7; j++) { if (day > 0 && day <= daysInMonth) { data[i][j] = day; } else { data[i][j] = ""; } day++; } } calendarTable.setModel(new javax.swing.table.DefaultTableModel(data, columnNames)); calendarTable.setDefaultRenderer(calendarTable.getColumnClass(0), new CalendarCellRenderer()); } private class CalendarCellRenderer extends DefaultTableCellRenderer { @Override public Component getTableCellRendererComponent(JTable table, Object value, boolean isSelected, boolean hasFocus, int row, int column) { JLabel label = (JLabel) super.getTableCellRendererComponent(table, value, isSelected, hasFocus, row, column); if (value != null) { int day = (int) value; if (day == LocalDate.now().getDayOfMonth() && currentYearMonth.equals(YearMonth.now())) { label.setForeground(Color.RED); } else { label.setForeground(table.getForeground()); } } return label; } } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable() { @Override public void run() { new CalendarApp().setVisible(true); } }); }}这个示例代码创建了一个带有窗体的日历应用，可以通过Prev和Next按钮切换月份。日历表格中，当前日期会以红色显示。
在这个示例代码中，我们使用了Swing的JFrame、JLabel、JButton、JTable等组件来构建窗体和日历表格。updateCalendar()方法用于更新日历表格的内容。CalendarCellRenderer类用于自定义单元格的渲染，以便高亮显示当前日期。
通过运行main()方法，可以启动日历应用并显示窗体。
