//打印指定年月的日历
public class PrintCalendar {
 
 public static void main(String[] args) {
 int year=2013;
 int month=12;
 printMonth(year,month);
 }
 
 private static void printMonth(int year, int month) {//打印日历
 printMonthTitle(year,month);
 printMonthBody(year,month);
 }
 
 private static void printMonthTitle(int year, int month) {//打印日历标题
 System.out.println("   "+getMonthName(month)+" "+year);
 System.out.println("------------------------------");
 System.out.println(" Sun Mon Tue Wed Thu Fri Sat");
 }
 
 private static String getMonthName(int month) {
 String monthName=null;
 switch(month){
 case 1:monthName="January";break;
 case 2:monthName="February";break;
 case 3:monthName="March";break;
 case 4:monthName="April";break;
 case 5:monthName="May";break;
 case 6:monthName="June";break;
 case 7:monthName="July";break;
 case 8:monthName="August";break;
 case 9:monthName="September";break;
 case 10:monthName="October";break;
 case 11:monthName="November";break;
 case 12:monthName="December";
 }
 return monthName;
 }
 
 public static boolean isLeapYear(int year){//判断是否为闰年
 return year%400==0||(year%4==0&&year%100!=0);
 }
 
 public static int getNumberOfDaysInMonth(int year,int month){//获取对应月份天数
 if(month==1||month==3||month==5||month==7||month==8||month==10||month==12)
  return 31;
 if(month==4||month==6||month==9||month==11)
  return 30;
 if(month==2)
  return isLeapYear(year)?29:28;
 return 0;
 }
 
 public static int getTotalNumberOfDays(int year,int month){//获取从1800年到当月的总天数
 int total=0;
 for(int i=1800;i<year;i++){
  if(isLeapYear(i))
  total=total+366;
  else
  total=total+365;
 }
 for(int i=1;i<month;i++)
  total=total+getNumberOfDaysInMonth(year,i);
 return total;
 }
 
 public static int getStartDay(int year,int month){//获得当月第一天是星期几
 int startDay1800=3;
 int totalNumberOfDays=getTotalNumberOfDays(year,month);
 return (totalNumberOfDays+startDay1800)%7;
 }
 
 public static void printMonthBody(int year,int month){//打印日历体
 int startDay=getStartDay(year,month);
 int numberOfDaysInMonth=getNumberOfDaysInMonth(year,month);
 for(int i=0;i<startDay;i++){
  System.out.print("  ");
 }
 for(int i=1;i<=numberOfDaysInMonth;i++){
  if(i<10)
  System.out.print("  "+i);
  else
  System.out.print(" "+i);
  if((i+startDay)%7==0)
  System.out.println();
 }
 System.out.println();
 }
}