From http://www.deadcoderising.com/java-8-no-more-loops/

Article.java

private class Article {

    private final String title;
    private final String author;
    private final List<String> tags;

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

    public String getTitle() {
        return title;
    }

    public String getAuthor() {
        return author;
    }

    public List<String> getTags() {
        return tags;
    }
}

Flat map solution.java

public Set<String> getDistinctTags() {  
    return articles.stream()
        .flatMap(article -> article.getTags().stream())
        .collect(Collectors.toSet());
}

Map with Stream.java

public Map<String, List<Article>> groupByAuthor() {  
    return articles.stream()
        .collect(Collectors.groupingBy(Article::getAuthor));
}    

Second Stream solution.java

public List<Article> getAllJavaArticles() {  
    return articles.stream()
        .filter(article -> article.getTags().contains("Java"))
        .collect(Collectors.toList());
    }

Second traditional for loop.java

public List<Article> getAllJavaArticles() {

    List<Article> result = new ArrayList<>();

    for (Article article : articles) {
        if (article.getTags().contains("Java")) {
            result.add(article);
        }
    }

    return result;
}

Stream solution.java

public Optional<Article> getFirstJavaArticle() {  
    return articles.stream()
        .filter(article -> article.getTags().contains("Java"))
        .findFirst();
    }

traditional Loop 3.java

public Set<String> getDistinctTags() {

    Set<String> result = new HashSet<>();

    for (Article article : articles) {
        result.addAll(article.getTags());
    }

    return result;
}

traditional loop.java

public Article getFirstJavaArticle() {

    for (Article article : articles) {
        if (article.getTags().contains("Java")) {
            return article;
        }
    }

    return null;
}

Traditional Map for loop.java

public Map<String, List<Article>> groupByAuthor() {

    Map<String, List<Article>> result = new HashMap<>();

    for (Article article : articles) {
        if (result.containsKey(article.getAuthor())) {
            result.get(article.getAuthor()).add(article);
        } else {
            ArrayList<Article> articles = new ArrayList<>();
            articles.add(article);
            result.put(article.getAuthor(), articles);
        }
    }

    return result;
}