adding hours in date time format java

Question

SimpleDateFormat parser = new SimpleDateFormat(\"HH:mm\");
Date time1 = parser.parse(\"7:30\");

Now if I want to add 2 more hours to time1

Answer 1

tl;dr

LocalTime.parse( "07:30" ).plusHours( 2 )

…or…

ZonedDateTime.now( ZoneId.of( " Pacific/Auckland" ) )
    .plusHours( 2 )

java.time

The old date-time classes such as java.util.Date, .Calendar, and java.text.SimpleDateFormat should be avoided, now supplanted by the java.time classes.

LocalTime

For a time-of-day only value, use the LocalTime class.

LocalTime lt = LocalTime.parse( "07:30" );
LocalTime ltLater = lt.plusHours( 2 );  
String output = ltLater.toString();  // 09:30

Instant

For a given java.util.Date, convert to java.time using new methods added to the old classes. The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds.

Instant instant = myUtilDate.toInstant();

Or capture current moment in UTC as an Instant.

Instant instant = Instant.now();

Add two hours as seconds. The TimeUnit class can convert hours to seconds.

long seconds = TimeUnit.HOURS.toSeconds( 2 );
Instant instantLater = instant.plusSeconds( seconds );

ZonedDateTime

To view in the wall-clock time of some community, apply a time zone. Apply a ZoneId to get a ZonedDateTime object.

ZoneId z = ZoneId.of( "America/Montreal" );
ZonedDateTime zdt = instant.atZone( z );

You can add hours. The ZonedDateTime class handles anomalies such as Daylight Saving Time.

ZonedDateTime zdtLater = zdt.plusHours( 2 );

Duration

You can represent that two hours as an object.

Duration d = Duration.ofHours( 2 ) ;
ZonedDateTime zdtLater = zdt.plus( d ) ;