Sometimes you want to change the time of localDateTime, but Calendar can only change the information of date. You need to convert date to localDateTime or change localDateTime to date.

//date->localDateTime
Instant.ofEpochMilli(date.getTime()).atZone(ZoneId.systemDefault()).toLocalDateTime()
//localDateTime->date
Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant());