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

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

参考资料: https://docs.oracle.com/javase/7/docs/api/java/util/Calendar.html