Java Streams: filter().count() vs anyMatch()

Question

I want to find if a stream of strings has at least one occurrence of another String in a Set<String>. I came up with two solutions.

Performance wise, which approach is the best/recommended?

1)

return source.stream().filter(this::streamFilter).count() > 0;

2)

return source.stream().anyMatch(this::streamFilter);

Here's streamFilter method:

private boolean streamFilter(String str) {
    return filterKeywords.contains(str.toLowerCase());
}

filterKeywords: private Set<String> filterKeywords;

Or is there better approach than this?

Answer 1

You should use anyMatch(this::streamFilter), look at the API on the anyMatch method below (emphasis mine) as it may not evaluate all elements of the stream where as count() obviously iterates the whole stream of elements.

Returns whether any elements of this stream match the provided predicate. May not evaluate the predicate on all elements if not necessary for determining the result. If the stream is empty then false is returned and the predicate is not evaluated.

The point is some of the stream methods like findFirst(), anyMatch(), findAny(), etc.. perform short-circuiting operations i.e., they may not evaluate all elements of the stream and you can refer here for more details.

Answer 2

anyMatch doesn't always execute all the stream. It is the best approach.