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Java Java Data Structures Exploring the Java Collection Framework Sets

I did import requierd statements yet it is giving me an error

Im getting error of "import correct statements", which i have done already. Plus im confused as to how set the return type of the type as List<BlogPost> /<String> or Set<BlogPost>/Set<String> ??

package com.example;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

public class BlogPost implements Comparable<BlogPost>, Serializable {
  private String mAuthor;
  private String mTitle;
  private String mBody;
  private String mCategory;
  private Date mCreationDate;

  public BlogPost(String author, String title, String body, String category, Date creationDate) {
    mAuthor = author;
    mTitle = title;
    mBody = body;
    mCategory = category;
    mCreationDate = creationDate;

  public int compareTo(BlogPost other) {
    if (equals(other)) {
      return 0;
    return mCreationDate.compareTo(other.mCreationDate);

  public String[] getWords() {
    return mBody.split("\\s+");

  public List<String> getExternalLinks() {
    List<String> links = new ArrayList<String>();
    for (String word : getWords()) {
      if (word.startsWith("http")) {
    return links;

  public String getAuthor() {
    return mAuthor;

  public String getTitle() {
    return mTitle;

  public String getBody() {
    return mBody;

  public String getCategory() {
    return mCategory;

  public Date getCreationDate() {
    return mCreationDate;
package com.example;

import java.util.List;
import java.util.Set;
import java.util.HashSet;

public class Blog {
  List<BlogPost> mPosts;

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

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

  public List<String> getAllAuthors(){

    SortedSet<String> authors = new HashSet<String>();
    for(BogPost author:posts){


    return authors;

1 Answer

Kourosh Raeen
Kourosh Raeen
23,733 Points

Here are the problems I see in the code:

  1. According to the instructions, the method should return a Set, but you're returning a List.

  2. Since you need this set of authors to be sorted use a TreeSet as the implementation of your set.

  3. In the for loop change the variable author to post since you are looping over all the posts. Also, the posts are in the member variable mPosts so in the for loop posts should be mPosts:

for(BlogPost post: mPosts){
  1. In the body of the loop you need to get the author of the current post, post.getAuthor(), and add it to the authors TreeSet. Since you are adding the authors one by one you should use the add() method instead of addAll().

Let me know if you have any more question.

Thats solved my problem. Thank you so much !!