Java 日历 类与实例
Java中的日历类是一个抽象类，它提供了在一个特定的时间瞬间和一组日历字段（如月、年、小时）之间转换日期的方法。它继承了Object类并实现了Comparable, Serializable, Cloneable接口。
由于它是一个抽象类，所以我们不能使用构造函数来创建一个实例。相反，我们将不得不使用静态方法Calendar.getInstance()来实例化和实现一个子类。
Calendar.getInstance(): 返回一个基于默认时区的当前时间的Calendar实例，并使用默认区域设置。Calendar.getInstance(TimeZone zone)Calendar.getInstance(Locale aLocale)Calendar.getInstance(TimeZone zone, Locale aLocale)用 Java程序来演示getInstance()方法
// Date getTime(): It is used to return a// Date object representing this// Calendar's time value. import java.util.*;public class Calendar1 { public static void main(String args[]) { Calendar c = Calendar.getInstance(); System.out.println("The Current Date is:" + c.getTime()); }}
输出:
The Current Date is:Tue Aug 28 11:10:40 UTC 2018
重要的方法和它们的用途
| 方法 | 描述 |
|---|---|
| abstract void add(int field, int amount) | 它用于根据日历的规则，在给定的日历字段中添加或减去指定的时间量。 |
| int get(int field) | 它用于返回给定的日历字段的值。 |
| abstract int getMaximum(int field) | 用于返回该日历实例中给定日历字段的最大值。 |
| abstract int getMinimum(int field) | 用于返回该日历实例中给定日历字段的最小值。 |
| Date getTime() | 它用于返回一个代表此《日历》时间值的Date对象。 |
下面的程序说明了上述方法。
程序1 ：演示get()方法的Java程序。
// Program to demonstrate get() method// of Calendar class import java.util.*;public class Calendar2 { public static void main(String[] args) { // creating Calendar object Calendar calendar = Calendar.getInstance(); // Demonstrate Calendar's get()method System.out.println("Current Calendar's Year: " + calendar.get(Calendar.YEAR)); System.out.println("Current Calendar's Day: " + calendar.get(Calendar.DATE)); System.out.println("Current MINUTE: " + calendar.get(Calendar.MINUTE)); System.out.println("Current SECOND: " + calendar.get(Calendar.SECOND)); }}
输出:
Current Calendar's Year: 2018Current Calendar's Day: 28Current MINUTE: 10Current SECOND: 45
程序2 ：演示getMaximum()方法的Java程序。
// Program to demonstrate getMaximum() method// of Calendar class import java.util.*;public class Calendar3 { public static void main(String[] args) { // creating calendar object Calendar calendar = Calendar.getInstance(); int max = calendar.getMaximum(Calendar.DAY_OF_WEEK); System.out.println("Maximum number of days in a week: " + max); max = calendar.getMaximum(Calendar.WEEK_OF_YEAR); System.out.println("Maximum number of weeks in a year: " + max); }}输出:
Maximum number of days in a week: 7Maximum number of weeks in a year: 53
程序3 ：演示getMinimum()方法的Java程序。
// Program to demonstrate getMinimum() method// of Calendar class import java.util.*;public class Calendar4 { public static void main(String[] args) { // creating calendar object Calendar calendar = Calendar.getInstance(); int min = calendar.getMinimum(Calendar.DAY_OF_WEEK); System.out.println("Minimum number of days in week: " + min); min = calendar.getMinimum(Calendar.WEEK_OF_YEAR); System.out.println("Minimum number of weeks in year: " + min); }}输出:
Minimum number of days in week: 1Minimum number of weeks in year: 1
程序4 ：演示add()方法的Java程序。
// Program to demonstrate add() method// of Calendar class import java.util.*;public class Calendar5 { public static void main(String[] args) { // creating calendar object Calendar calendar = Calendar.getInstance(); calendar.add(Calendar.DATE, -15); System.out.println("15 days ago: " + calendar.getTime()); calendar.add(Calendar.MONTH, 4); System.out.println("4 months later: " + calendar.getTime()); calendar.add(Calendar.YEAR, 2); System.out.println("2 years later: " + calendar.getTime()); }}输出:
15 days ago: Mon Aug 13 11:10:57 UTC 20184 months later: Thu Dec 13 11:10:57 UTC 20182 years later: Sun Dec 13 11:10:57 UTC 2020
参考资料: https://docs.oracle.com/javase/7/docs/api/java/util/Calendar.html
