概述
The <code>Calendar</code> class is an abstract class that provides methods for converting between a specific instant in time and a set of {@link #fields calendar fields} such as <code>YEAR</code>, <code>MONTH</code>, <code>DAY_OF_MONTH</code>, <code>HOUR</code>, and so on, and for manipulating the calendar fields, such as getting the date of the next week.
An instant in time can be represented by a millisecond value that is an offset from the <a name="Epoch"><em>Epoch</em></a>, January 1, 1970 00:00:00.000 GMT (Gregorian).
Calendar是一个抽象类；
作用： time 与 Calendar的YEAR、MONTH等的转换 以及 用于操作Calendar字段的方法；
time用ms表示，该值是一个相对于标准时间（1970 年 1 月 1 日 00:00:00.000 GMT）的偏移量；
The class also provides additional fields and methods for implementing a concrete calendar system outside the package.
Those fields and methods are defined as <code>protected</code>.
Calendar也提供了额外的字段&方法，用于在包外实现calendar；
Like other locale-sensitive classes, <code>Calendar</code> provides a class method, <code>getInstance</code>, for getting a generally useful object of this type.
<code>Calendar</code>'s <code>getInstance</code> method returns a <code>Calendar</code> object whose calendar fields have been initialized with the current date and time:
Calendar提供了getInstance方法，用于获取Calendar（字段已被当前time初始化）；
public abstract class Calendar implements Serializable, Cloneable, Comparable<java.util.Calendar> {
protected long time;
public int get(int field)
{
complete();
return internalGet(field);
}
public static Calendar getInstance()
{
return createCalendar(TimeZone.getDefault(), Locale.getDefault(Locale.Category.FORMAT));
}
public final Date getTime() {
return new Date(getTimeInMillis());
}
public long getTimeInMillis() {
if (!isTimeSet) {
updateTime();
}
return time;
}
}
方法
get
time与Calendar的YEAR、MONTH等的转换
Calendar calendar = Calendar.getInstance();
int i = calendar.get(Calendar.YEAR);
int i1 = calendar.get(Calendar.MONTH);
int i2 = calendar.get(Calendar.DATE);
int i3 = calendar.get(Calendar.HOUR);
int i4 = calendar.get(Calendar.MINUTE);
int i5 = calendar.get(Calendar.SECOND);
System.out.println(i + "-" + i1+ "-" + i2+ " " + i3+ ":" + i4+ ":" + i5); // 2023-11-20 10:52:47
int i6 = calendar.get(Calendar.WEEK_OF_YEAR);
int i7 = calendar.get(Calendar.DAY_OF_YEAR);
System.out.println(i6 + " " + i7);
int i8 = calendar.get(Calendar.WEEK_OF_MONTH);
int i9 = calendar.get(Calendar.DAY_OF_MONTH);
System.out.println(i8 + " " + i9);
int i10 = calendar.get(Calendar.DAY_OF_WEEK);
int i11 = calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH);
set
为 年、月、日、时、分、秒 设置指定的值；
Calendar calendar1 = Calendar.getInstance();
calendar1.set(2001, Calendar.OCTOBER,23,12,23,54);
Date time = calendar1.getTime();
System.out.println(time); // Tue Oct 23 12:23:54 CST 2001
String format1 = DateFormat.getDateTimeInstance().format(time);
System.out.println(format1); // 2001-10-23 12:23:54