Java中的 Date before() 方法及示例

Java Date 类的before()方法测试日期是否早于指定日期。

句法：

public boolean before(Date when)

参数：该函数接受单个参数when指定必须检查的日期。

返回值：它返回一个布尔值。如果此日期早于指定日期，它将返回 true，否则返回 false。

异常：如果when为 null，该函数将抛出一个NullPointerException异常。

下面的程序演示了上述函数：

// Java code to demonstrate
// before() 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);
  
        System.out.println("Is Date 2 before Date 1: "
                         + currentDate.before(dateOne));
    }
}

输出：

Date 1: Thu Dec 05 08:15:01 UTC 1996
Date 2: Wed Jan 02 08:15:01 UTC 2019
Is Date 2 before Date 1: false

// Java code to demonstrate
// before() function of Date class
  
import java.util.Date;
  
public class GfG {
    // main method
    public static void main(String[] args)
    {
  
        // creating a date of object
        // storing the current date
        Date currentDate = new Date();
  
        System.out.println("Date 1: " + currentDate);
  
        // specifiedDate is assigned to null.
        Date specifiedDate = null;
  
        System.out.println("Date 1: " + specifiedDate);
  
        System.out.println("On checking these 2 dates: ");
  
        try {
            // throws NullPointerException
            System.out.println(currentDate
                                   .before(specifiedDate));
        }
        catch (Exception e) {
            System.out.println("Exception: " + e);
        }
    }
}

输出：

Date 1: Wed Jan 02 08:15:06 UTC 2019
Date 1: null
On checking these 2 dates: 
Exception: java.lang.NullPointerException