Java AWT 簡易萬年曆實作

使用 java.awt 元件建立視窗式萬年曆，包含月份、年份下拉選單、日期按鈕網格。透過 GregorianCalendar 計算每月天數與起始星期，動態更新按鈕標籤。程式碼雖使用舊版 AWT API，但邏輯清晰，適合初學者理解事件驅動與日期計算。

import java.awt.*;
import java.awt.event.*;
import java.util.*;

public class CalendarCreator extends Frame {
    Button[] days = new Button[49];
    Choice monthChoice = new Choice();
    Choice yearChoice = new Choice();
    Label lMonth = new Label("MONTH");
    Label lYear = new Label("Year");
    Label lText = new Label("YEAR UPTO:::");
    Panel p1, p2;
    GregorianCalendar gc = new GregorianCalendar();
    int totDays;
    TextField textField = new TextField(2);

    public CalendarCreator() {
        setTitle("Calendar");
        setSize(400, 400);
        setResizable(false);
        setLocation(50, 50);
        p1 = new Panel(new FlowLayout());
        p2 = new Panel(new GridLayout(7, 7, 10, 10));
        p1.setBackground(Color.red);
        p2.setBackground(Color.cyan);
        add(p1, BorderLayout.NORTH);
        add(p2);

        p1.add(lText); p1.add(textField);
        p1.add(lMonth); p1.add(monthChoice);
        String[] months = {"JAN","FEB","MAR","APR","MAY","JUN","JUL","AUG","SEP","OCT","NOV","DEC"};
        for (String m : months) monthChoice.add(m);
        monthChoice.addItemListener(new MyListener(this));

        textField.addActionListener(new MyAction(this));

        p1.add(lYear); p1.add(yearChoice);
        yearChoice.add("1990");
        yearChoice.addItemListener(new MyListener(this));

        for (int i = 0; i < 49; i++) days[i] = new Button("");
        for (int c = 0; c < 49; c++) p2.add(days[c]);

        setVisible(true);
    }

    void setYear(String newYear) {
        int y = Integer.parseInt(newYear);
        for (int i = 1991; i <= y; i++) yearChoice.add(String.valueOf(i));
    }

    void setButtons(int startDay, int totalDays) {
        int idx = 7;
        String[] week = {"SUN","MON","TUE","WED","THUR","FRI","SAT"};
        for (int i = 0; i < 7; i++) days[i].setLabel(week[i]);
        for (int i = 0; i < startDay; i++, idx++) days[idx].setLabel("");
        for (int d = 1; d <= totalDays; d++, idx++) days[idx].setLabel(String.valueOf(d));
        while (idx < 49) days[idx++].setLabel("");
    }

    void setVal(Date date, int day, int selMonth, int selYear) {
        gc.setTime(date);
        if (selMonth==0||selMonth==2||selMonth==4||selMonth==6||selMonth==7||selMonth==9||selMonth==11) totDays=31;
        else if (selMonth==3||selMonth==5||selMonth==8||selMonth==10) totDays=30;
        else if (gc.isLeapYear(selYear)) totDays=29;
        else totDays=28;
        setButtons(day, totDays);
    }

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

class MyListener implements ItemListener {
    CalendarCreator cal;
    MyListener(CalendarCreator c) { cal = c; }
    public void itemStateChanged(ItemEvent e) {
        int m = cal.monthChoice.getSelectedIndex();
        int y = Integer.parseInt(cal.yearChoice.getSelectedItem()) - 1900;
        Date d = new Date(y, m, 1);
        cal.setVal(d, d.getDay(), m, y);
    }
}

class MyAction implements ActionListener {
    CalendarCreator cal;
    MyAction(CalendarCreator c) { cal = c; }
    public void actionPerformed(ActionEvent e) {
        String s = cal.textField.getText();
        cal.setYear(s);
        ((TextField)e.getSource()).removeActionListener(this);
    }
}

改進建議：

• 改用 Swing 元件 (JFrame, JComboBox, JButton) 取代 AWT，獲得更好的跨平台外觀。
• Date 建構子與 getDay() 已過時，建議改用 Calendar 或 java.time.YearMonth。
• 年份輸入可加入驗證，避免非數字導致例外。