用java语言，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。

好的，我会尽力回答你的问题。首先，我们可以使用Java Swing GUI框架来实现月历的设计。下面是一个示例代码：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Calendar;

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

public class MonthCalendar extends JFrame implements ActionListener {

    private static final long serialVersionUID = 1L;
    private JLabel monthLabel;
    private JButton previousButton, nextButton;
    private JPanel calendarPanel;
    private Container container;
    private Calendar calendar;
    private int year, month, day;

    public MonthCalendar() {
        super("Month Calendar");

        container = getContentPane();
        container.setLayout(new BorderLayout());

        // 创建月份标签
        monthLabel = new JLabel("", JLabel.CENTER);
        monthLabel.setForeground(Color.BLUE);

        // 创建日历面板
        calendarPanel = new JPanel(new GridLayout(0, 7));
        calendarPanel.setBorder(BorderFactory.createLineBorder(Color.BLACK));

        // 创建上一个月按钮
        previousButton = new JButton("<<");
        previousButton.addActionListener(this);

        // 创建下一个月按钮
        nextButton = new JButton(">>");
        nextButton.addActionListener(this);

        // 添加组件到窗体
        container.add(monthLabel, BorderLayout.NORTH);
        container.add(calendarPanel, BorderLayout.CENTER);
        container.add(previousButton, BorderLayout.WEST);
        container.add(nextButton, BorderLayout.EAST);

        // 设置窗口属性
        setSize(400, 300);
        setVisible(true);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // 初始化日历
        calendar = Calendar.getInstance();
        year = calendar.get(Calendar.YEAR);
        month = calendar.get(Calendar.MONTH);
        day = calendar.get(Calendar.DATE);
        updateCalendar(year, month);
    }

    /**
     * 更新日历面板
     * 
     * @param year
     * @param month
     */
    private void updateCalendar(int year, int month) {
        calendar.set(year, month, 1);
        int firstDayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);
        int daysInMonth = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);

        // 清空原有组件
        calendarPanel.removeAll();

        // 添加星期标签
        String[] weekDays = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
        for (int i = 0; i < weekDays.length; i++) {
            JLabel weekLabel = new JLabel(weekDays[i], JLabel.CENTER);
            weekLabel.setFont(new Font("Serif", Font.BOLD, 14));
            calendarPanel.add(weekLabel);
        }

        // 填充日历面板
        for (int i = 1; i < firstDayOfWeek; i++) {
            calendarPanel.add(new JLabel(""));
        }
        for (int i = 1; i <= daysInMonth; i++) {
            JButton dayButton = new JButton(Integer.toString(i));
            dayButton.setFont(new Font("Serif", Font.PLAIN, 14));
            dayButton.setPreferredSize(new Dimension(50, 50));
            dayButton.addActionListener(new DateActionListener(i));
            calendarPanel.add(dayButton);
        }

        // 更新月份标签
        monthLabel.setText(year + "-" + (month + 1));
    }

    /**
     * 上一个月按钮事件处理
     */
    private void previousButtonActionPerformed() {
        if (month == 0) {
            year -= 1;
            month = 11;
        } else {
            month -= 1;
        }
        updateCalendar(year, month);
    }

    /**
     * 下一个月按钮事件处理
     */
    private void nextButtonActionPerformed() {
        if (month == 11) {
            year += 1;
            month = 0;
        } else {
            month += 1;
        }
        updateCalendar(year, month);
    }

    /**
     * 日期按钮事件处理
     */
    private class DateActionListener implements ActionListener {

        private int day;

        public DateActionListener(int day) {
            this.day = day;
        }

        public void actionPerformed(ActionEvent e) {
            System.out.println(year + "-" + (month + 1) + "-" + day);
        }
    }

    /**
     * 按钮事件处理
     */
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == previousButton) {
            previousButtonActionPerformed();
        } else if (e.getSource() == nextButton) {
            nextButtonActionPerformed();
        }
    }

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

}

上述代码实现了一个基本的月历，包括月份标签、日历面板、上一个月按钮、下一个月按钮等组件。通过`updateCalendar()`方法可以更新日历面板，通过`previousButtonActionPerformed()`和`nextButtonActionPerformed()`方法可以切换月份，通过`DateActionListener`类可以处理日期按钮的事件。你可以根据自己的需求进行修改和扩展。