Java如何计算两个日期之间相差天数呢?

计算两个日期之间相隔天数的实现思路

1.获取两个日期的毫秒数
2.减去毫秒数,然后除以相应的秒数得到之间相隔的天数

 
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class TestClass {
    /**
     * @param args
     * @throws ParseException 
     */
    public static void main(String[] args) throws ParseException {
        // TODO Auto-generated method stub
        SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date d1=sdf.parse("2023-05-08 12:10:10");
        Date d2=sdf.parse("2023-05-15 02:00:00");
        System.out.println(daysBetween(d1,d2));

        System.out.println(daysBetween("2023-05-08 12:10:10","2023-05-15 02:00:00"));
    }
    
    /** 
     * 计算两个日期之间相差的天数 
     * @param smdate 较小的时间
     * @param bdate  较大的时间
     * @return 相差天数
     * @throws ParseException 
     */  
    public static int daysBetween(Date smdate,Date bdate) throws ParseException  
    {  
        SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
        smdate=sdf.parse(sdf.format(smdate));
        bdate=sdf.parse(sdf.format(bdate));
        Calendar cal = Calendar.getInstance();  
        cal.setTime(smdate);  
        long time1 = cal.getTimeInMillis();               
        cal.setTime(bdate);  
        long time2 = cal.getTimeInMillis();       
        long between_days=(time2-time1)/(1000*3600*24);
          
       return Integer.parseInt(String.valueOf(between_days));         
    }  
    
　　/**
　　 *字符串的日期格式的计算
　　 */
    public static int daysBetween(String smdate,String bdate) throws ParseException{
        SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
        Calendar cal = Calendar.getInstance();  
        cal.setTime(sdf.parse(smdate));  
        long time1 = cal.getTimeInMillis();               
        cal.setTime(sdf.parse(bdate));  
        long time2 = cal.getTimeInMillis();       
        long between_days=(time2-time1)/(1000*3600*24);
          
       return Integer.parseInt(String.valueOf(between_days));   
    }
}