Java 日历 before()方法

java.util.Calendar.before()是java.util包中 Calendar 类的一个方法。如果这个Calendar所代表的时间在 when Object所代表的时间之前，该方法返回true。如果不是这种情况，则返回false。

语法:

public boolean before(Object when)

Where, **when** is the Object 
that is to be compared.

下面是一些例子，以更好地理解Calendar.before()函数的实现。

例子1 :

// Implementation to show the usage
// of before(Object when) method of
// Calendar class
import java.util.*;
  
class GFG {
  
    public static void main(String[] args)
        throws InterruptedException
    {
  
        // creating calendar object
        Calendar cal_obj1 = Calendar.getInstance();
  
        // printing current date
        System.out.println("Time 1 : " + cal_obj1.getTime());
  
        // sleep for 3 seconds
        Thread.sleep(3000);
  
        // creating Calendar object
        Calendar cal_obj2 = Calendar.getInstance();
  
        // printing current date
        System.out.println("Time 2 : " + cal_obj2.getTime());
  
        // checking if 1st date is before 2nd date
        // and printing the result
        System.out.println(cal_obj1.before(cal_obj2));
    }
}

输出:

Time 1 : Wed Feb 28 15:43:19 IST 2018
Time 2 : Wed Feb 28 15:43:22 IST 2018
true

例2 :

// Implementation to show the usage
// of before(Object when) method of
// Calendar class
import java.util.*;
  
class GFG {
  
    public static void main(String[] args)
    {
  
        // creating calendar objects
        Calendar cal_obj1 = Calendar.getInstance();
        Calendar cal_obj2 = Calendar.getInstance();
  
        // displaying the current date
        System.out.println("Current date is : " + cal_obj1.getTime());
  
        // changing year in cal_obj2 calendar
        cal_obj2.set(Calendar.YEAR, 2010);
  
        // displaying the year
        System.out.println("Year is " + cal_obj2.get(Calendar.YEAR));
  
        // check if calendar date is before current date
        System.out.println("Result : " + cal_obj1.before(cal_obj2));
    }
}

输出:

Current date is : Wed Feb 28 15:50:16 IST 2018
Year is 2010
Result : false

例3 :

// Implementation to show the usage
// of before(Object when) method of
// Calendar class
import java.util.*;
  
class GFG {
  
    public static void main(String[] args)
    {
  
        // creating calendar objects
        Calendar cal_obj1 = Calendar.getInstance();
        Calendar cal_obj2 = Calendar.getInstance();
  
        // displaying the current date
        System.out.println("Current date is : " + cal_obj1.getTime());
  
        // changing year in cal_obj2 calendar
        cal_obj2.set(Calendar.YEAR, 2025);
  
        // displaying the year
        System.out.println("Year is " + cal_obj2.get(Calendar.YEAR));
  
        // check if calendar date is before current date
        System.out.println("Result : " + cal_obj1.before(cal_obj2));
    }
}

输出:

Current date is : Wed Feb 28 16:15:55 IST 2018
Year is 2025
Result : true