Java's one of the worst language examples of using FP collections I've seen. Even with hindsight I still find this to be uglier and unnecessarily more verbose than it needs to be.

E.g. same Example in Dart:

    class Article {
      String title;
      String author;
      List<String> tags;
      Article(this.title, this.author, this.tags);  
    }

    Article getFirstJavaArticle() =>
        articles.firstWhere((x) => x.tags.contains("Java"));

    List<Article> getAllJavaArticles() =>
        articles.where((x) => x.tags.contains("Java"));

    List<String> getDistinctTags() =>
        articles.expand((x) => x.tags).toSet().toList();

Can even be shorter without the Optional typing, but it's more readable to be explicit to have them. Dart benefits from having Collection and Stream mixins so you always get a rich API on Dart's collections.

If anyone's interested to comparing FP collections in different languages, I've ported C# 101 LINQ examples in:

  - Swift    https://github.com/mythz/swift-linq-examples
  - Clojure  https://github.com/mythz/clojure-linq-examples
  - Dart     https://github.com/dartist/101LinqSamples