Java中的日历类和示例

Java中的Calendar类是一个抽象类，它提供了在特定时刻和一组日历字段（如MONTH、YEAR、HOUR等）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()：根据默认时区的当前时间，使用默认语言环境返回一个 Calendar 实例。
Calendar.getInstance(TimeZone 区域)
Calendar.getInstance(Locale aLocale)
Calendar.getInstance(TimeZone zone, Locale aLocale)

演示 getInstance() 方法的Java程序：

// 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

重要方法及其用法

METHOD	DESCRIPTION
abstract void add(int field, int amount)	It is used to add or subtract the specified amount of time to the given calendar field, based on the calendar’s rules.
int get(int field)	It is used to return the value of the given calendar field.
abstract int getMaximum(int field)	It is used to return the maximum value for the given calendar field of this Calendar instance.
abstract int getMinimum(int field)	It is used to return the minimum value for the given calendar field of this Calendar instance.
Date getTime()	It is used to return a Date object representing this Calendar’s time value.

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: 2018
Current Calendar's Day: 28
Current MINUTE: 10
Current 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: 7
Maximum 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: 1
Minimum 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 2018
4 months later: Thu Dec 13 11:10:57 UTC 2018
2 years later: Sun Dec 13 11:10:57 UTC 2020

参考： https: Java/util/Calendar.html