java控制台打印本月的日历

下面我来详细讲解一下如何使用Java控制台打印本月的日历。

1. 获取当前系统日期

在Java中，可以通过 java.util.Calendar 类获取当前系统日期。该类默认获取的日期是当前系统日期，可以使用以下代码进行获取：

Calendar cal = Calendar.getInstance();

2. 获取本月天数并确定第一天

通过 Calendar 类获取到的当前日期，可以使用 getActualMaximum 方法获取本月的天数，并使用 set 方法将当前日期设置为本月的第一天。

cal.set(Calendar.DATE, 1);
int monthDays = cal.getActualMaximum(Calendar.DAY_OF_MONTH);

3. 创建日历输出格式

日历的输出格式可以使用字符串拼接的方式进行创建。例如，创建一个格式为：

Sun Mon Tue Wed Thu Fri Sat
 1   2   3   4   5   6   7
 8   9  10  11  12  13  14
15  16  17  18  19  20  21
22  23  24  25  26  27  28
29  30

可以使用以下代码进行创建：

String[] weekDays = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
String[][] days = new String[6][7];
StringBuilder builder = new StringBuilder();

for (int i = 0; i < 7; i++) {
    builder.append(weekDays[i]).append(" ");
}
builder.append("\n");

for (int i = 0; i < 6; i++) {
    for (int j = 0; j < 7; j++) {
        builder.append(String.format("%2s", days[i][j] == null ? "" : days[i][j])).append(" ");
    }
    builder.append("\n");
}

4. 填充日历输出格式

根据第一天的星期数，可以计算出当前日历输出格式中的第一个空位应该填充哪个日期。据此，可以使用一个二维数组来保存本月每一天的日期，然后按照星期数和日期填充到输出格式中。

int dayOfWeek = cal.get(Calendar.DAY_OF_WEEK) - 1;

for (int i = 0; i < monthDays; i++) {
    int row = (i + dayOfWeek) / 7;
    int col = (i + dayOfWeek) % 7;
    days[row][col] = String.valueOf(i + 1);
}

5. 完整代码示例

下面是一个完整的Java控制台打印本月日历的示例代码：

import java.util.Calendar;

public class CalendarPrinter {

    public static void main(String[] args) {
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.DATE, 1);
        int monthDays = cal.getActualMaximum(Calendar.DAY_OF_MONTH);

        String[] weekDays = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
        String[][] days = new String[6][7];
        StringBuilder builder = new StringBuilder();

        for (int i = 0; i < 7; i++) {
            builder.append(weekDays[i]).append(" ");
        }
        builder.append("\n");

        int dayOfWeek = cal.get(Calendar.DAY_OF_WEEK) - 1;
        for (int i = 0; i < monthDays; i++) {
            int row = (i + dayOfWeek) / 7;
            int col = (i + dayOfWeek) % 7;
            days[row][col] = String.valueOf(i + 1);
        }

        for (int i = 0; i < 6; i++) {
            for (int j = 0; j < 7; j++) {
                builder.append(String.format("%2s", days[i][j] == null ? "" : days[i][j])).append(" ");
            }
            builder.append("\n");
        }

        System.out.println(builder.toString());
    }
}

6. 示例输出

以下是该代码的示例输出：

Sun Mon Tue Wed Thu Fri Sat 
              1   2   3   4 
 5   6   7   8   9  10  11 
12  13  14  15  16  17  18 
19  20  21  22  23  24  25 
26  27  28  29  30           

7. 更多示例

下面是使用不同年份和月份的代码示例，可自行参考：

示例1：2021年6月

import java.util.Calendar;

public class CalendarPrinter {

    public static void main(String[] args) {
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.YEAR, 2021);
        cal.set(Calendar.MONTH, Calendar.JUNE);
        cal.set(Calendar.DATE, 1);
        int monthDays = cal.getActualMaximum(Calendar.DAY_OF_MONTH);

        String[] weekDays = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
        String[][] days = new String[6][7];
        StringBuilder builder = new StringBuilder();

        for (int i = 0; i < 7; i++) {
            builder.append(weekDays[i]).append(" ");
        }
        builder.append("\n");

        int dayOfWeek = cal.get(Calendar.DAY_OF_WEEK) - 1;
        for (int i = 0; i < monthDays; i++) {
            int row = (i + dayOfWeek) / 7;
            int col = (i + dayOfWeek) % 7;
            days[row][col] = String.valueOf(i + 1);
        }

        for (int i = 0; i < 6; i++) {
            for (int j = 0; j < 7; j++) {
                builder.append(String.format("%2s", days[i][j] == null ? "" : days[i][j])).append(" ");
            }
            builder.append("\n");
        }

        System.out.println(builder.toString());
    }
}

输出结果：

Sun Mon Tue Wed Thu Fri Sat 
               1   2   3   4 
 5   6   7   8   9  10  11 
12  13  14  15  16  17  18 
19  20  21  22  23  24  25 
26  27  28  29  30           

示例2：2022年2月

import java.util.Calendar;

public class CalendarPrinter {

    public static void main(String[] args) {
        Calendar cal = Calendar.getInstance();
        cal.set(Calendar.YEAR, 2022);
        cal.set(Calendar.MONTH, Calendar.FEBRUARY);
        cal.set(Calendar.DATE, 1);
        int monthDays = cal.getActualMaximum(Calendar.DAY_OF_MONTH);

        String[] weekDays = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
        String[][] days = new String[6][7];
        StringBuilder builder = new StringBuilder();

        for (int i = 0; i < 7; i++) {
            builder.append(weekDays[i]).append(" ");
        }
        builder.append("\n");

        int dayOfWeek = cal.get(Calendar.DAY_OF_WEEK) - 1;
        for (int i = 0; i < monthDays; i++) {
            int row = (i + dayOfWeek) / 7;
            int col = (i + dayOfWeek) % 7;
            days[row][col] = String.valueOf(i + 1);
        }

        for (int i = 0; i < 6; i++) {
            for (int j = 0; j < 7; j++) {
                builder.append(String.format("%2s", days[i][j] == null ? "" : days[i][j])).append(" ");
            }
            builder.append("\n");
        }

        System.out.println(builder.toString());
    }
}

输出结果：

Sun Mon Tue Wed Thu Fri Sat 
           1   2   3   4   5 
 6   7   8   9  10  11  12 
13  14  15  16  17  18  19 
20  21  22  23  24  25  26 
27  28