[JAVA] Set the time of LocalDateTime to a specific time

Date Time API added from Java 8. In the code written using LocalDateTime in this, I sometimes see such code.

Set each field one by one.java

LocalDateTime ldt = LocalDateTime.now().withHour(12).withMinute(0).withSecond(0).withNano(0);

The setting is like "Today's 12 o'clock", but each field of time is set one by one. Well, when I used Calendar, it was basically one by one, so it may have happened in the flow. However, this is inefficient because a new instance is created each time withXxx ().

LocalDateTime # with is used in such cases. That's right.

public LocalDateTime with(TemporalAdjuster adjuster) Returns an adjusted copy of this date / time. It adjusts the date / time and returns a LocalDateTime based on this date / time. Adjustments are made using the specified adjuster strategy object. Please refer to the adjuster documentation to understand what adjustments will be made.

I'm not very familiar with TemporalAdjuster, but here I will simply introduce the following usage.

Set at 12 o'clock in one shot.java

LocalDateTime ldt = LocalDateTime.now().with(LocalTime.of(12, 0));

LocalTime also implements this TemporalAdjuster, so you can pass it to the with method. And it changes the time of the instance of LocalDateTime to the time of the argument.

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