// Add the companion creative to the creative set.
creativeSet.setCompanionCreativeIds(
Longs.concat(creativeSet.getCompanionCreativeIds(), new long[] {companionCreativeId}));
// Update the creative set on the server.
CreativeSet updatedCreativeSet = creativeSetService.updateCreativeSet(creativeSet);
System.out.printf("A creative set with ID \"%d\", master creative ID \"%d\", "
+ "and companion creative IDs [%s] was updated.", updatedCreativeSet.getId(),
updatedCreativeSet.getMasterCreativeId(),
Longs.join(",", updatedCreativeSet.getCompanionCreativeIds()));