java 计算2个日期的时间差

//计算秒
public static void main(String[] args) throws  Exception{
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.ENGLISH);
    Date firstDate = sdf.parse("2019-07-25 10:00:00");
    Date secondDate = sdf.parse("2019-07-25 11:00:00");

    long diffInMillis = Math.abs(secondDate.getTime() - firstDate.getTime());
    long diff = TimeUnit.SECONDS.convert(diffInMillis, TimeUnit.MILLISECONDS);
    System.out.println(diff);

}

//计算分钟
public static void main(String[] args) throws  Exception{
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.ENGLISH);
    Date firstDate = sdf.parse("2019-07-25 10:00:00");
    Date secondDate = sdf.parse("2019-07-25 11:00:00");

    long diffInMillis = Math.abs(secondDate.getTime() - firstDate.getTime());
    long diff = TimeUnit.MINUTES.convert(diffInMillis, TimeUnit.MILLISECONDS);
    System.out.println(diff);

}

//计算天

public static void main(String[] args) throws  Exception{
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.ENGLISH);
    Date firstDate = sdf.parse("2019-07-25 10:00:00");
    Date secondDate = sdf.parse("2019-07-25 11:00:00");

    long diffInMillis = Math.abs(secondDate.getTime() - firstDate.getTime());
    long diff = TimeUnit.DAYS.convert(diffInMillis, TimeUnit.MILLISECONDS);
    System.out.println(diff);

}