Question

new data:

ArrayList<Comment> newComments =  getComments();

already existing data, has some data already filled in:

ArrayList<Comment> oldComments 

I can’t overwrite entire old contents with new ones.

I want new (not already present) Comment objects in newComments to be added to oldComments, also I want those missing in newComments to be removed from oldComments.

Is there some good method in Collections package for this ? or any other way ?

NOTE: Comment class has custom compare() method (not using default equals() )

Answer 1

A java.util.Set is more appropriate for your use case. Then you can do:

oldComments.retainAll(newComments);
oldComments.addAll(newComments);