Change Type of Method Reference

Joka Lee :

My code:

class BlogPost {
    String title;
    String author;
    BlogPostType type;
    int likes;

    public BlogPost(String title, String author, BlogPostType type, int likes) {
        this.title = title;
        this.author = author;
        this.type = type;
        this.likes = likes;
    }
//getter setter
}

and:

public enum BlogPostType {
    NEWS,
    REVIEW,
    GUIDE
}

and:

public static void main(String[] args) {
        List<BlogPost> posts = Arrays.asList(new BlogPost("Start Java", "Ram", BlogPostType.NEWS, 11),
            new BlogPost("Start Java 8", "Rajou", BlogPostType.REVIEW, 101),
            new BlogPost("Functional programming", "Das", BlogPostType.REVIEW, 111),
            new BlogPost("Lambda", "Ramos", BlogPostType.GUIDE, 541));

        Map<BlogPostType, List<BlogPost>> Blist = posts.stream().collect(groupingBy(BlogPost::getType));
        System.out.println(Blist);
}}

I have three classes one is BlogPost , BlogPostType and Main.

I am making a map of Map<BlogPostType, List<BlogPost>> Blist by using groupingBy() and it works perfectly fine. i used a method reference there BlogPost::getType , i can use lambda expression also (x) -> x.getType().

But when i try to change the type of Map , i.e Map<String, List<BlogPost>> Blist1 then i cannot use Method reference. Is there any possible way to use method reference and get the type also changed??

I am thinking why cant we use like this: BlogPost::getType.toString() or (String)BlogPost::getType while we can do this in lambda (x) -> x.getType().toString(). Any possible ways to use Method reference and get along with conversion of type also?

Adrian :

you can use Function.identity() to chain method references (as many as you want). For example, put the following function in groupingBy:

Function.<BlogPost>identity()
        .andThen(BlogPost::getType)
        .andThen(BlogPostType::toString)

but it's better to use lambda