今天是2018年11月7号，学习了一下calendar类。下面的代码让我百思不得其解。
import java.util.Calendar;
import java.util.GregorianCalendar;
public class TestCalendar {
public static void main(String[] args) {
Calendar calendar=new GregorianCalendar(2018,11,7,15,58,32);//我以为是表示2018年11月7日15:58:32
System.out.println(calendar.get(Calendar.DAY_OF_WEEK));//
}
}
今天是星期三，但是输出的值为6。想了许久，原来calendar的月份是从0开始的，所以11表示12月份，问题就出在了这里。这个calendar类的源码有定义：
/**
* Value of the {@link #MONTH} field indicating the
* first month of the year in the Gregorian and Julian calendars.
*/
public static final int JANUARY = 0;
/**
* Value of the {@link #MONTH} field indicating the
* second month of the year in the Gregorian and Julian calendars.
*/
public static final int FEBRUARY = 1;
/**
* Value of the {@link #MONTH} field indicating the
* third month of the year in the Gregorian and Julian calendars.
*/
public static final int MARCH = 2;
/**
* Value of the {@link #MONTH} field indicating the
* fourth month of the year in the Gregorian and Julian calendars.
*/
public static final int APRIL = 3;
/**
* Value of the {@link #MONTH} field indicating the
* fifth month of the year in the Gregorian and Julian calendars.
*/
public static final int MAY = 4;
/**
* Value of the {@link #MONTH} field indicating the
* sixth month of the year in the Gregorian and Julian calendars.
*/
public static final int JUNE = 5;
/**
* Value of the {@link #MONTH} field indicating the
* seventh month of the year in the Gregorian and Julian calendars.
*/
public static final int JULY = 6;
/**
* Value of the {@link #MONTH} field indicating the
* eighth month of the year in the Gregorian and Julian calendars.
*/
public static final int AUGUST = 7;
/**
* Value of the {@link #MONTH} field indicating the
* ninth month of the year in the Gregorian and Julian calendars.
*/
public static final int SEPTEMBER = 8;
/**
* Value of the {@link #MONTH} field indicating the
* tenth month of the year in the Gregorian and Julian calendars.
*/
public static final int OCTOBER = 9;
/**
* Value of the {@link #MONTH} field indicating the
* eleventh month of the year in the Gregorian and Julian calendars.
*/
public static final int NOVEMBER = 10;
/**
* Value of the {@link #MONTH} field indicating the
* twelfth month of the year in the Gregorian and Julian calendars.
*/
public static final int DECEMBER = 11;
/**
* Value of the {@link #MONTH} field indicating the
* thirteenth month of the year. Although
GregorianCalendar* does not use this value, lunar calendars do.
*/
将代码改成如下：
import java.util.Calendar;
import java.util.GregorianCalendar;
public class TestCalendar {
public static void main(String[] args) {
Calendar calendar=new GregorianCalendar(2018,10,7,15,58,32);//表示2018年11月7日15:58:32
System.out.println(calendar.get(Calendar.DAY_OF_WEEK));//
}
}
输出结果为4，（我们想要3，但是第一天默认是星期天）。这个也是calender源码里面设置的：
/**
* Value of the {@link #DAY_OF_WEEK} field indicating
* Sunday.
*/
public static final int SUNDAY = 1;
/**
* Value of the {@link #DAY_OF_WEEK} field indicating
* Monday.
*/
public static final int MONDAY = 2;
/**
* Value of the {@link #DAY_OF_WEEK} field indicating
* Tuesday.
*/
public static final int TUESDAY = 3;
/**
* Value of the {@link #DAY_OF_WEEK} field indicating
* Wednesday.
*/
public static final int WEDNESDAY = 4;
/**
* Value of the {@link #DAY_OF_WEEK} field indicating
* Thursday.
*/
public static final int THURSDAY = 5;
/**
* Value of the {@link #DAY_OF_WEEK} field indicating
* Friday.
*/
public static final int FRIDAY = 6;
/**
* Value of the {@link #DAY_OF_WEEK} field indicating
* Saturday.
*/
public static final int SATURDAY = 7;