Java Java Data Structures Exploring the Java Collection Framework Sets

michael lee
michael lee
5,176 Points

what am I doing wrong?

Am I missing something?

com/example/BlogPost.java
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 {
  public 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")) {
        links.add(word);
      }
    }
    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;
  }
}
com/example/Blog.java
package com.example;
import java.util.Set;
import java.util.TreeSet;
import java.util.List;

public class Blog {
  List<BlogPost> mPosts;

  public Set<String> getAllAuthors(){
    Set<String> authors = new TreeSet<>();
    for(String author : getAuthor()){
      authors.add(author);
    }

  return authors;
  }

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

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

1 Answer

Hi. The problem is with your for loop.

Here we have 2 classes: a BlogPost object (with author, title, body, category and creationDate) and a Blog object (a list of BlogPosts, called mPosts).

Where do we get the authors from? We get them from the BlogPost object. So you want to iterate through each blogpost in that blogpost list (mPosts) and get the author from each of them. Then add that author to the author List.

public Set<String> getAllAuthors() {
        Set<String> authors = new TreeSet<>();
        for (BlogPost blogPost : mPosts) {
            authors.add(blogPost.getAuthor());
        }
        return authors;
}

It reads: "For each blogpost in the mPosts list of blogposts, get the author and add it to the author Set. Then returns the Set." Hope that helps :)

michael lee
michael lee
5,176 Points

thanks a lot, that really helps ~~

You're welcome :)