java - How to get maximum value from of the first N values of an ArrayList?

Question

There is an ArrayList which stores integer values. Suppose the arrayList stored values are: 10, 20, 30, 40, 50.

I know how to find the maximum value of the collection. I would have to do:

Collections.max(arrayList); 

But what should I do to find the maximum of the first 3 elements of the collection? So in this example, it would be 30. Is there a sublist function for collections?

question from:https://stackoverflow.com/questions/65926838/how-to-get-maximum-value-from-of-the-first-n-values-of-an-arraylist

Answer 1

List has a subList method that you can use:

Collections.max(arrayList.subList(0, 3))

There is no subList for Collections in general, as not all collections are lists and, for some, the "first N elements" doesn't make a lot of sense, as they don't maintain any meaningful order (e.g. HashSet).

You can take the first three elements of any Collection (in whatever order the collection will provide), by iterating through it with a limit. It's probably best to use a stream for this:

yourCollection.stream().limit(3).collect(Collectors.toList());

Or you can find what you're looking for directly on the stream, without collecting the elements in some collection:

Optional<Integer> max = yourCollection.stream.limit(3).max(Comparator.naturalOrder());