Java中的日期 compareTo() 方法及示例

Java Date 类的compareTo()方法比较两个日期并对它们进行排序。

句法：

public int compareTo(Date anotherDate)

参数：该函数接受一个参数anotherDate ，它指定要比较的日期。

返回值：该函数给出以下指定的三个返回值：

• 如果参数 Date 等于此 Date，则返回值 0。
• 如果此 Date 在 Date 参数之前，则返回小于 0 的值。
• 如果此 Date 在 Date 参数之后，则返回大于 0 的值。

异常：如果anotherDate为空，该函数将引发一个异常，即NullPointerException 。

下面的程序演示了上述函数：

// Java code to demonstrate
// compareTo() function of Date class
  
import java.util.Date;
import java.util.Calendar;
public class GfG {
    // main method
    public static void main(String[] args)
    {
  
        // creating a Calendar object
        Calendar c = Calendar.getInstance();
  
        // set Month
        // MONTH starts with 0 i.e. ( 0 - Jan)
        c.set(Calendar.MONTH, 11);
  
        // set Date
        c.set(Calendar.DATE, 05);
  
        // set Year
        c.set(Calendar.YEAR, 1996);
  
        // creating a date object with specified time.
        Date dateOne = c.getTime();
  
        System.out.println("Date 1: "
                           + dateOne);
  
        // creating a date of object
        // storing the current date
        Date currentDate = new Date();
  
        System.out.println("Date 2: "
                           + currentDate);
  
        // compares
        System.out.println("On Comparison: "
                           + currentDate
                                 .compareTo(dateOne));
    }
}

输出：

Date 1: Thu Dec 05 08:17:55 UTC 1996
Date 2: Wed Jan 02 08:17:55 UTC 2019
On Comparison: 1

// Java code to demonstrate
// compareTo() function of Date class
  
import java.util.Date;
  
public class GfG {
    // main method
    public static void main(String[] args)
    {
  
        // creating a date of object
        // stospecified datent date
        Date currentDate = new Date();
  
        System.out.println("Date 1: " + currentDate);
  
        // specifiedDate is assigned to null.
        Date specifiedDate = null;
  
        System.out.println("Date 2: " + specifiedDate);
  
        System.out.println("Passing null as parameter: ");
        try {
            // throws NullPointerException
            System.out.println(currentDate
                                   .compareTo(specifiedDate));
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

输出：

Date 1: Wed Jan 02 08:18:02 UTC 2019
Date 2: null
Passing null as parameter: 
Exception: java.lang.NullPointerException