java编写应用程序，有一个窗口，该窗口的布局为BorderLayout布局。窗口的中心添加一个JPanel容器pCenter,pCenter的布局是7行7列的GriderLayout布局，pCenter中放置49个标签，用来显示日历。窗口的上面添加一个JPane容器pNorth,其布局是FlowLayout布局，pNorth放置两个按钮：nextMonth和previousMonth。单击后分别显示下一月和上一月的日历。窗口下面添加一个JPanel容器pSouth，其布局是FlowLayout布局，pSouth中放置一个标签用来显示一些信息。界面如下图所示。

这是一个比较典型的Java GUI程序的设计，需要使用Swing组件进行实现。以下是代码示例：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.GridLayout;

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

public class CalendarGUI extends JFrame {
    private static final long serialVersionUID = 1L;
    private JPanel pCenter, pNorth, pSouth;
    private JLabel[] days;
    private JLabel infoLabel;
    private JButton nextMonthButton, previousMonthButton;
    private int currentMonth, currentYear;

    public CalendarGUI() {
        super("Calendar");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(500, 500);

        // Center panel
        pCenter = new JPanel(new GridLayout(7, 7));
        days = new JLabel[49];
        for (int i = 0; i < 49; i++) {
            days[i] = new JLabel("", SwingConstants.CENTER);
            days[i].setBorder(BorderFactory.createLineBorder(Color.BLACK));
            if (i < 7) {
                days[i].setText(getWeekday(i));
                days[i].setForeground(Color.BLUE);
            } else {
                days[i].setFont(new Font("Arial", Font.PLAIN, 16));
            }
            pCenter.add(days[i]);
        }
        displayCalendar(2021, 9);

        // North panel
        pNorth = new JPanel(new FlowLayout());
        nextMonthButton = new JButton("Next Month");
        nextMonthButton.addActionListener(e -> {
            if (currentMonth == 12) {
                displayCalendar(currentYear + 1, 1);
            } else {
                displayCalendar(currentYear, currentMonth + 1);
            }
        });
        previousMonthButton = new JButton("Previous Month");
        previousMonthButton.addActionListener(e -> {
            if (currentMonth == 1) {
                displayCalendar(currentYear - 1, 12);
            } else {
                displayCalendar(currentYear, currentMonth - 1);
            }
        });
        pNorth.add(previousMonthButton);
        pNorth.add(nextMonthButton);

        // South panel
        pSouth = new JPanel(new FlowLayout());
        infoLabel = new JLabel("Some information here");
        pSouth.add(infoLabel);

        // Add panels to frame
        add(pNorth, BorderLayout.NORTH);
        add(pCenter, BorderLayout.CENTER);
        add(pSouth, BorderLayout.SOUTH);

        setVisible(true);
    }

    private void displayCalendar(int year, int month) {
        currentYear = year;
        currentMonth = month;

        // Update center panel
        for (int i = 7; i < 49; i++) {
            days[i].setText("");
        }
        int firstDayOfWeek = getFirstDayOfWeek(year, month);
        int numDays = getNumDaysInMonth(year, month);
        for (int i = 1; i <= numDays; i++) {
            days[firstDayOfWeek + i - 1].setText("" + i);
        }

        // Update info label
        String monthName = getMonthName(month);
        infoLabel.setText(monthName + " " + year);
    }

    private String getWeekday(int index) {
        String[] weekdays = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
        return weekdays[index];
    }

    private String getMonthName(int month) {
        String[] months = { "January", "February", "March", "April", "May", "June", "July", "August", "September",
                "October", "November", "December" };
        return months[month - 1];
    }

    private int getFirstDayOfWeek(int year, int month) {
        java.util.Calendar cal = java.util.Calendar.getInstance();
        cal.set(year, month - 1, 1);
        return cal.get(java.util.Calendar.DAY_OF_WEEK) - 1;
    }

    private int getNumDaysInMonth(int year, int month) {
        java.util.Calendar cal = java.util.Calendar.getInstance();
        cal.set(year, month - 1, 1);
        return cal.getActualMaximum(java.util.Calendar.DAY_OF_MONTH);
    }

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

这个程序使用了Java的Lambda表达式来简化事件处理器的编写。在代码中，`displayCalendar`方法用于根据给定的年份和月份更新日历视图，`getFirstDayOfWeek`和`getNumDaysInMonth`方法用于计算月份中第一天是周几和该月的天数。`getWeekday`和`getMonthName`方法用于获取星期几和月份名称的文本。