Is there a performance gain by using lambda expressions?

ycr :

I have a requirement to check whether there is a common element in two lists. I came up with two ways to do this:

Method 01 : Loops

private boolean func01 (List<String> list1, List<String> list2) {
    for (String group : list1) {
        for (String funcGroup : list2) {
            if (group.equals(funcGroup)) {
                return true;
            }
        }
    }
    return false;
}

Method 02 : Lambda

private boolean func02 (List<String> list1, List<String> list2) {
    return list1.stream().filter(list2::contains).findAny().isPresent();
}

In my view, I find the first method more readable. What I need to understand is, whether there are any differences or advantages when comparing these two methods?

hovanessyan :

method 1 optimization:

you don't need 2 loops and you can return immediately when you have a match, so you stop the traversing of the list at that point - (e.g. sunshine case you get a match on first element - you have 1 iteration, worst case your match is the last element - you have to traverse the whole list to hit that match)

private boolean func01 (List<String> list1, List<String> list2) {
        for (String group : list1) {
            if (list2.contains(group)) return true;
        }

        return false;
    }

lambda equivalent optimization:

• findAny().isPresent() - get an optional of an element matching the predicate and check if the Optional is present - this is equivalent of anyMatch() because both expressions return boolean

• filter() will always traverse the whole list

• anyMatch() has a short-circuit behavior - means it will stop on the first match

so you can re-write it as:

private boolean func02 (List<String> list1, List<String> list2) {
  return list1.stream().anyMatch(list2::contains);
}

To answer your question - there's no significant performance difference in the two approaches, but take into consideration:

• creating stream for a collection has a slight overhead

• stream operations can be run in parallel (list1.stream().parallel().anyMatch(list2::contains)). For example in this case anyMatch() running in parallel threads over the same stream will periodically check if the previous threads found a match and will stop traversing the collection and not continue traversing the whole collection. So in theory for significantly large input lists, you should get better results with parallel streams.

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