《CORE JAVA》日历程序的代码注释 CalendarText.java

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import java.text.DateFormatSymbols;
import java.util.*;

/**
* @version 1.4 2007-04-07
* @author Cay Horstmann
*/

public class CalendarTest
{
   public static void main(String[] args)
   {
      // construct d as current date
    Locale.setDefault(Locale.US);

      GregorianCalendar d = new GregorianCalendar();
      int today = d.get(Calendar.DAY_OF_MONTH);
      int month = d.get(Calendar.MONTH);
//     System.out.println("today is :"+today);
//     System.out.println("month is :"+month);//注意：month从0开始计算的，即一月份对应0
      // set d to start date of the month

      d.set(Calendar.DAY_OF_MONTH, 1);
      //设置d为当前的第一天


      int weekday = d.get(Calendar.DAY_OF_WEEK);
      //获得当前第一天所对应的星期几

      // get first day of week (Sunday in the U.S.)
      int firstDayOfWeek = d.getFirstDayOfWeek();
      //获得当前地区星期的起始日

      // determine the required indentation for the first line
      int indent = 0;
      while (weekday != firstDayOfWeek)
      {
         indent++;
         d.add(Calendar.DAY_OF_MONTH, -1);
         //将当前日历对象的日减少1，直到一个星期的第一天为止
         weekday = d.get(Calendar.DAY_OF_WEEK);
      }

      // print weekday names
      String[] weekdayNames = new DateFormatSymbols().getShortWeekdays();
      do
      {
   //此时d指向一周的第一天即对应sunday的日子，所以下面第一句输出地weekdayNames对应为sunday
         System.out.printf("%4s", weekdayNames[weekday]);
//此时d指向下一天即对应monday的日子
         d.add(Calendar.DAY_OF_MONTH, 1);

         weekday = d.get(Calendar.DAY_OF_WEEK);

      }
      while (weekday != firstDayOfWeek);
      System.out.println();
//此处为打印星期几的结尾，接下来的程序为打印从星期日到本月第一天之间的空格
      for (int i = 1; i <= indent; i++)
         System.out.print("    ");
//the end of the print of the xingqiji

      d.set(Calendar.DAY_OF_MONTH, 1); //d指向本月第一天
      do                                 //程序开始正式打印日期
      {
         // print day
         int day = d.get(Calendar.DAY_OF_MONTH); //获得本月第一天的日期并且打印
         System.out.printf("%3d", day);

         // mark current day with *
         if (day == today) System.out.print("*"); //如果打印到了今天那么就在day后添加*
         else System.out.print(" ");//如果打印到了不是今天那么就在day后什么都不添加只打印日期号码

         // advance d to the next day
         d.add(Calendar.DAY_OF_MONTH, 1);//将d指向下一天
         weekday = d.get(Calendar.DAY_OF_WEEK);//获得下一天的星期数

         // start a new line at the start of the week
         if (weekday == firstDayOfWeek) System.out.println();
      }
      while (d.get(Calendar.MONTH) == month);//当d不再指向本月时候跳出循环
      // the loop exits when d is day 1 of the next month

      // print final end of line if necessary
    if (weekday != firstDayOfWeek) System.out.println();
   }
二、最终调试结果

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 31

三、调试过程中遇到的问题

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 31

如上所示：对应的错误原因：

for (int i = 1; i <= indent; i++)
System.out.print("");

由于System.out.printf("%4s", weekdayNames[weekday]);中对应定义了每一个为4个字符的长度，对应print输出地字符串中没有空出4个空格，进行正确的移位

修改方法：

for (int i = 1; i <= indent; i++)
System.out.print(" ");

从而可以实现最终的调试结果