java的 before_Java Date before()用法及代码示例

Java Date类的before()方法测试日期是否在指定的日期之前。

用法:

public boolean before(Date when)

参数：该函数接受一个参数，该参数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，该函数将引发单个异常，该异常为NullPointerException。

下面的程序演示了上述功能：

// 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