How can simple calendar functionality be implemented in Java?

To implement basic calendar functionality, you can utilize the Calendar class and SimpleDateFormat class built into Java.

First, you can create a Calendar object and set the date to the first day of the month you want to display. For example, to display the calendar of the current month, you can use the following code:

Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.DAY_OF_MONTH, 1);

Next, you can determine the day of the week for the first day of the month and adjust the calendar display format accordingly. For example, Sunday can be considered the first day of the week, Monday can be considered the first day of the week, and so on. You can use the following code to get the day of the week:

int firstDayOfWeek = calendar.get(Calendar.DAY_OF_WEEK);

Then, you can determine the number of rows and columns displayed on the calendar, and create a two-dimensional array to store the dates. Typically, a calendar has 6 rows and 7 columns. You can use the following code to create a two-dimensional array.

int[][] calendarMatrix = new int[6][7];

Next, you can use a loop to populate a two-dimensional array and store dates at each position. You can achieve this using the following code:

int currentDay = 1;
for (int i = 0; i < 6; i++) {
    for (int j = 0; j < 7; j++) {
        if (i == 0 && j < firstDayOfWeek - 1) {
            // 如果是第一行，且不在第一天之后，则填充0
            calendarMatrix[i][j] = 0;
        } else if (currentDay <= calendar.getActualMaximum(Calendar.DAY_OF_MONTH)) {
            // 填充日期
            calendarMatrix[i][j] = currentDay;
            currentDay++;
        }
    }
}

Finally, you can use a loop to print the two-dimensional array in order to display the calendar. You can use the following code to accomplish this:

System.out.println("日 一 二 三 四 五 六");
for (int i = 0; i < 6; i++) {
    for (int j = 0; j < 7; j++) {
        System.out.print(calendarMatrix[i][j]);
        System.out.print(" ");
    }
    System.out.println();
}

By doing this, you can achieve basic calendar functionality. You can modify and expand the code as needed, such as adding the functionality to input a year and month in order to display the calendar for a specific month.