Question

hi i’ve seen this post how to implement the union and intersection when it you have two sets of data,that are strings.how can i do the same when my sets contain objects,and i want to get the union of only one property of each object?

Answer 1

But I want to override them somehow so that it wont add an object if there’s an object already in my set that has the same value in a selected property.If i’m not clear enough tell me so i can write an example.

I think the best way to do this is to use a ConcurrentMap.

ConcurrentMap<String, MyType> map = new ConcurrentHashMap<>();

// the collection to retain.
for(MyType mt: retainedSet) map.put(mt.getKey(), mt);

// the collection to keep if not duplicated
for(MyType mt: onlyIfNewSet) map.putIfAbsent(mt.getKey(), mt);

// to get the intersection.
Set<String> toKeep = new HashSet<>();
for(MyType mt: onlyIfNewSet) toKeep.add(mt.getKey());

// keep only the keys which match.
map.keySet().retainAll(toKeep);