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Java Java Data Structures - Retired Exploring the Java Collection Framework Sets

Posted by nobodyinhere
nobodyinhere
3,418 Points

Stuck on Sets and Collections Challenge

I can't figure out what exactly we should do in Sets. Also I guess I can't understand the fundamentals of Generics and Collections. I tried many different things but in every time I got some console errors. I understood the example in Video but Still can't do it for BlogPost code series. Maybe I can figure out when I understood what should I do with loops and returning "java.util.Set" of all the authors.

Also We have to sort them alphabetically with TreeSet<String> but when I created new one, I got some critical errors with syntax. What should i do?

Here is task:

I've added a new class called Blog. It is initialized with a list of blog posts. Create a method in the Blog class called getAllAuthors that loops all the posts and returns a java.util.Set of all the authors. They should be sorted alphabetically.

2 Answers

Ken Alger
STAFF
Ken Alger
Treehouse Teacher
Ken Alger
Ken Alger
Treehouse Teacher

Abdullah;

Let's have a look.

Challenge

I've added a new class called Blog. It is initialized with a list of blog posts. Create a method in the Blog class called getAllAuthors that loops all the posts and returns a java.util.Set of all the authors. They should be sorted alphabetically.

Let me lay out my strategy on this and you can have another go at it with coding it out.

  1. Create the getAllAuthors method... should be a public method that returns a Set.
  2. Define a working variable. Since it will be what we are returning it needs to be a Set. Since it will be a set of authors, that sounds like it needs to be a Set<String>. Probably need to make sure we import java.util.Set. That will be our interface.
  3. Since we are wanting to have the authors returned in alphabetical order, if we implement a TreeSet, like you mentioned in your post, we can get that. Probably need to make sure we import java.util.TreeSet.
  4. Need to cast our working variable to TreeSet, something like Set<String> authors = new TreeSet<String>().
  5. Loop through our posts (mPosts) and extract the author from the post and add it to our working set.
  6. Return our data.

See if that gets you headed in the correct direction and post back if you are still stuck.

Happy coding,

Ken

nobodyinhere
nobodyinhere
3,418 Points

I guess I can't understand this stage. Where is my fault?

This is my Blog.java

package com.example;

import java.util.List;
import java.util.Set;
import java.util.TreeSet;

public class Blog {
  List<BlogPost> mPosts;

  public Blog(List<BlogPost> posts) {
    mPosts = posts;
  }

  public List<BlogPost> getPosts() {
    return mPosts;
  }

  public Set<BlogPost> getAllAuthors(){
    Set authors = new TreeSet();

      for (String post : mPosts) {
        authors.add(post);
    }
    return authors;
  }
}

/* my getAllAuthors() Method.

 public Set<BlogPost> getAllAuthors(){
    Set authors = new TreeSet();

      for (String post : mPosts) {
        authors.add(post);
    }
    return authors;
  }

*/
Yigit Cakar
PLUS
Yigit Cakar
Courses Plus Student 5,975 Points
Yigit Cakar
Yigit Cakar
Courses Plus Student 5,975 Points

Hello Abdullah,

Your method should return a set of strings. We are looping through BlogPosts and you forgot to extract the authors.

My getAllAuthors method is as follows:

public Set<String> getAllAuthors(){
    Set<String> authors = new TreeSet<String>();
    for (BlogPost posts:mPosts){
      authors.add(posts.getAuthor());
    }
    return authors;
  }
Yael P.
Yael P.
2,816 Points
Yael P.
Yael P.
2,816 Points

Hello Yigit,

Could you help me understand why your wrote (step by step):

  1. At the For loop mPosts and not getPosts()
  2. At the For loop statment ...(posts.getAuthor()); 
for (BlogPost posts:mPosts){
      authors.add(posts.getAuthor());
    }

Thanks, Yael

Pedro nieto Sanchez
Pedro nieto Sanchez
28,169 Points
Pedro nieto Sanchez
Pedro nieto Sanchez
28,169 Points

Hello Yael I think I might help you with this.

1.- Because mPosts has been defined inside the class. (Look at the first line inside the class) So you don't need the getPosts().

2.- Because Posts is each Object inside of the List<BlogPost> mPosts, therefore they all have available the method getaAuthor()