java中比较2个Date是不是同一天的五种实现方法与对比

import java.time.LocalDate;
import java.time.ZoneId;
import java.util.Date;

public boolean isSameDay(Date date1, Date date2) {
    LocalDate localDate1 = date1.toInstant()
        .atZone(ZoneId.systemDefault())
        .toLocalDate();
    LocalDate localDate2 = date2.toInstant()
        .atZone(ZoneId.systemDefault())
        .toLocalDate();
    return localDate1.isEqual(localDate2);
}

import java.time.Instant;
import java.time.LocalDate;
import java.time.ZoneId;
import java.util.Date;

public boolean isSameDay(Date date1, Date date2) {
    return LocalDate.ofInstant(date1.toInstant(), ZoneId.systemDefault())
        .equals(LocalDate.ofInstant(date2.toInstant(), ZoneId.systemDefault()));
}

import java.util.Calendar;
import java.util.Date;

public boolean isSameDay(Date date1, Date date2) {
    Calendar cal1 = Calendar.getInstance();
    Calendar cal2 = Calendar.getInstance();
    cal1.setTime(date1);
    cal2.setTime(date2);
    
    return cal1.get(Calendar.YEAR) == cal2.get(Calendar.YEAR) &&
           cal1.get(Calendar.MONTH) == cal2.get(Calendar.MONTH) &&
           cal1.get(Calendar.DAY_OF_MONTH) == cal2.get(Calendar.DAY_OF_MONTH);
}

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

public boolean isSameDay(Date date1, Date date2) {
    SimpleDateFormat fmt = new SimpleDateFormat("yyyyMMdd");
    return fmt.format(date1).equals(fmt.format(date2));
}

public boolean isSameDay(Date date1, Date date2) {
    return date1.toInstant().atZone(java.time.ZoneId.systemDefault()).toLocalDate()
        .equals(date2.toInstant().atZone(java.time.ZoneId.systemDefault()).toLocalDate());
}

public static void main(String[] args) {
    Date date1 = new Date();  // 当前时间
    Date date2 = new Date();  // 当前时间
    Date date3 = new Date(date1.getTime() + 24 * 60 * 60 * 1000);  // 明天
    
    System.out.println(isSameDay(date1, date2));  // true
    System.out.println(isSameDay(date1, date3));  // false
}