java日历如何让combox实现事件

问题遇到的现象和发生背景

java日历如何让combox实现事件

问题相关代码，请勿粘贴截图

import javax.swing.;
import java.awt.;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class RL
{

public RL()
{
    Date date=new Date();//获取日期
    int date_year=date.getYear()+1900;//获取年份
    int date_month=date.getMonth()+1;//获取月份
    CalendaBean cb = new CalendaBean();
    JPanel pSouth = new JPanel();

    final boolean[] todayFlag = {false};
    String year_int = null;
    int month_int;
    cb.setYear(date_year);
    cb.setMonth(date_month);
    JComboBox MonthBox = new JComboBox();
    JComboBox YearBox = new JComboBox();

    JFrame f=new JFrame();
    FlowLayout F=new FlowLayout(FlowLayout.CENTER);
    JPanel p=new JPanel(F);
   JLabel j1=new JLabel("年份：");
    JLabel j2=new JLabel("月份：");
    JLabel j3=new JLabel();
    JButton button=new JButton("确定");
    JButton button_today = new JButton("今天");


    JButton u=new JButton("上个月");
    JButton h=new JButton("下个月");
    u.setActionCommand("lastmonth");
    h.setActionCommand("nextmonth");
    u.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            cb.actionPerformed(e);
        }
    });

    h.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            cb.actionPerformed(e);
        }
    });
    p.add(j1);
    p.add(YearBox);
    p.add(j2);
    p.add(MonthBox);
    p.add(button);
    p.add(button_today);
    p.add(u);
    p.add(h);
    p.add(j3);
    this.setTimer(j3);
    GridLayout G=new GridLayout(7,7);
    JPanel p1=new JPanel(G);
    JLabel[] label;
    String[] a = cb.getCalendar();
    JButton week1 = new JButton("日");
    JButton week2 = new JButton("一");
    JButton week3 = new JButton("二");
    JButton week4 = new JButton("三");
    JButton week5 = new JButton("四");
    JButton week6 = new JButton("五");
    JButton week7 = new JButton("六");
    p1.add(week1);
    p1.add(week2);
    p1.add(week3);
    p1.add(week4);
    p1.add(week5);
    p1.add(week6);
    p1.add(week7);
    Font font = new Font("Dialog",Font.BOLD,12);
    u.setFont(font);
    h.setFont(font);
    for(int i = date_year - 20;i <= date_year + 100;i++){
        YearBox.addItem(i+"");
    }
    YearBox.setSelectedIndex(20);
    for(int i = 1;i < 13;i++){
        MonthBox.addItem(i+"");
    }
    MonthBox.setSelectedIndex(date_month-1);


    label = new JLabel[42];
    //for循环进行日期排序
    for (int i = 0; i < 42; i++) {
        label[i] = new JLabel();
        p1.add(label[i]);
    }
    cb.label = label;
    for (int i = 0; i < a.length; i++) {
        if (i % 7 == 0) {
            label[i].setText("");
        }
        label[i].setText("          "+a[i]);
    }
    p1.setLayout(G);
    f.add(p1,BorderLayout.CENTER);
    f.add(p,BorderLayout.NORTH);
    f.setSize(700,500);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setVisible(true);
    JLabel now = new JLabel();
    now.setText(""+cb.year+"年"+""+cb.month+"月");
    cb.now = now;
    pSouth.add(now);
    f.setLocationRelativeTo(null);
    f.add(pSouth, BorderLayout.SOUTH);
}

//动态时间线程
private void setTimer(JLabel j3)
{
    final JLabel varTime=j3;
    Timer timeAction=new Timer(100, new ActionListener()
    {
        @Override
        public void actionPerformed(ActionEvent e) {
            long timeillis=System.currentTimeMillis();
            SimpleDateFormat df=new SimpleDateFormat("yyyy年MM月dd日HH:mm:ss");
            varTime.setText(df.format(new Date(timeillis)));
        }
    }
    );
    timeAction.start();
}

//上下月翻页事件处理
class CalendaBean implements ActionListener {
JLabel[] label;
    JLabel now;
int year=0, month=0;
public void setYear(int year) {
    this.year = year;
}
public void setMonth(int month) {
    this.month = month;
}
public void actionPerformed(ActionEvent e) {
    String str = e.getActionCommand();

    if (str.equals("lastmonth")) {
        month--;
        if (month == 0) {
            month = 12;
            year--;
        }
    }
    else if (str.equals("nextmonth")) {
        month++;
        if (month == 13) {
            month = 1;
            year++;
        }
    }
    now.setText(""+year+"年"+""+month+"月");
    String[] a = getCalendar();
    for (int i = 0; i < a.length; i++) {
        if (i % 7 == 0) {
            label[i].setText("");
        }
        label[i].setText("          "+a[i]);
    }
}

public String[] getCalendar() {
    String[] a = new String[42];
    Calendar rili = Calendar.getInstance();
    rili.set(year, month - 1, 1);
    int weekDay = rili.get(Calendar.DAY_OF_WEEK) - 1;
    int day = 0;
    if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8
            || month == 10 || month == 12) {
        day = 31;
    }
    if (month == 4 || month == 6 || month == 9 || month == 11) {
        day = 30;
    }
    if (month == 2) {
        if ((year % 4 == 0) && (year % 100 != 0) || (year % 400 == 0))
            day = 29;
        else
            day = 28;
    }
    for (int i = 0; i < weekDay; i++)
        a[i] = "";
    for (int i = weekDay, n = 1; i < weekDay + day; i++) {
        a[i] = String.valueOf(n);
        n++;
    }
    for (int i = weekDay + day; i < a.length; i++)
        a[i] = "";
    return a;
}

}

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

}