Java - best way to compare two List<List<String>>?

Question

What's the best way to compare the String elements of two List<List<String>>...

At the end, I want to know if they contain the same elements (true) or not (false)

This two lists I want to compare:

ObservableList<List<String>> fnlData = FXCollections.observableList(new LinkedList<>());;

List<List<String>> fnlDataTMP = new LinkedList<>();

I searched for already answered questions in the forum, but nothing helped me ..

Answer 1

Try fnlData.equals(fnlDataTMP) if both list are in order

or if order does not matter, try creating hash set and then compare using equals

new HashSet(fnlData).equals(new HashSet(fnlDataTMP))

Answer 2

I don't think there is a way that let's you achieve that out of the box.

You can do something like the functional java List.join method to quickly generate 2 Lists and compare these:

List<String> joinedFnlData = jf.data.List.join(fnlData);
List<String> joinedFnlDataTMP = jf.data.List.join(fnlDataTMP);

CollectionUtils.isEqualCollection(joinedFnlData, joinedFnlDataTMP);

Things to note:

• This is probably not the cheapest operation - so it should not be invoked too often in a time critical scenario (e.g. UI thread)
• It does not do a "real" equals - for that you would have to do a nested loop like in the above answer. This checks that both joined lists have the same elements with the same cardinality: e.g. if fnlData has 2 lists with "1" and "2" as the only elements and fnlDataTMP has 1 list with "1", "2" as the elements, this would mark both as equal. Depending on your scenario this might be irrelevant - if this is relevant I don't see a way around nested loops.