据如下图，综合运用GUI编程、事件处理、Calendar类应用等知识设计 一款月历，要求能通过输入（或选择）年月的方式正确显示当前月份的所有日期。

以下是一个简单的Java月历程序，使用了Swing GUI库、ActionListener接口和Calendar类来实现。该程序可以根据用户输入的年份和月份生成并显示月历。

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Calendar;

import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class CalendarApp implements ActionListener {
    private JFrame frame;
    private JPanel monthPanel, yearPanel, datePanel;
    private JLabel monthLabel, yearLabel;
    private JComboBox<String> monthBox, yearBox;
    private JButton updateButton;

    public CalendarApp() {
        // 创建主窗口
        frame = new JFrame("月历");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 300);

        // 创建月份选择面板
        monthPanel = new JPanel();
        monthLabel = new JLabel("月份:");
        monthBox = new JComboBox<String>();
        for(int i = 1; i <= 12; i++) {
            monthBox.addItem(String.valueOf(i));
        }
        monthPanel.add(monthLabel);
        monthPanel.add(monthBox);

        // 创建年份选择面板
        yearPanel = new JPanel();
        yearLabel = new JLabel("年份:");
        yearBox = new JComboBox<String>();
        for(int i = 1900; i <= 2100; i++) {
            yearBox.addItem(String.valueOf(i));
        }
        yearPanel.add(yearLabel);
        yearPanel.add(yearBox);

        // 创建日期显示面板
        datePanel = new JPanel(new GridLayout(7, 7));
        updateCalendar(Calendar.getInstance());

        // 创建更新按钮
        updateButton = new JButton("更新");
        updateButton.addActionListener(this);

        // 将所有面板添加到主窗口中
        frame.add(monthPanel, BorderLayout.NORTH);
        frame.add(yearPanel, BorderLayout.CENTER);
        frame.add(datePanel, BorderLayout.SOUTH);
        frame.add(updateButton, BorderLayout.EAST);

        // 显示主窗口
        frame.setVisible(true);
    }

    // 更新月历
    private void updateCalendar(Calendar cal) {
        datePanel.removeAll();

        // 设置日期为当月1号
        cal.set(Calendar.DAY_OF_MONTH, 1);

        // 获取当月第一天是星期几
        int firstDayOfWeek = cal.get(Calendar.DAY_OF_WEEK);

        // 添加星期标签
        String[] weekDays = {"日", "一", "二", "三", "四", "五", "六"};
        for(int i = 0; i < weekDays.length; i++) {
            datePanel.add(new JLabel(weekDays[i], JLabel.CENTER));
        }

        // 添加日期
        for(int i = 1; i < firstDayOfWeek; i++) {
            datePanel.add(new JLabel(""));
        }
        int daysInMonth = cal.getActualMaximum(Calendar.DAY_OF_MONTH);
        for(int i = 1; i <= daysInMonth; i++) {
            datePanel.add(new JLabel(String.valueOf(i), JLabel.CENTER));
        }
        frame.validate();
    }

    // 处理更新按钮事件
    public void actionPerformed(ActionEvent e) {
        if(e.getSource() == updateButton) {
            int year = Integer.valueOf((String) yearBox.getSelectedItem());
            int month = Integer.valueOf((String) monthBox.getSelectedItem()) - 1;
            Calendar cal = Calendar.getInstance();
            cal.set(year, month, 1);
            updateCalendar(cal);
        }
    }

    public static void main(String[] args) {
        new CalendarApp();
    }
}

该程序包含三个面板：月份选择面板、年份选择面板和日期显示面板。月份和年份可以通过下拉框进行选择，日期显示面板根据用户选择的年份和月份显示当前月份的所有日期。用户可以点击“更新”按钮来更新月历。