SETS. Am doing something wrong, please help.

Question

I don't know what am doing wrong.

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 {
  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")) {
        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.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 List<Blog> getAllAuthors() {
    Set<String> allAuthors = new TreeSet<String>();
    for (Blog blog : posts) {
      allAuthors.addAll(posts.getAllAuthors());
    }
    return allAuthors;
  }
}

Answer 1 · 2015-10-28T22:33:17Z

October 28, 2015 10:33pm

Hey Yahya,

Let's go through each line that you have written:

youranswer.java

public List<Blog> getAllAuthors()

Re-read the question in the challenge. We want to return a java.util.Set of all the authors, which are stored as Strings. This is how it should look like. We return a set and pass in String as the generic value

answer.java

public Set<String> getAllAuthors()

Your next line is fine.

Let's look at this line:

youranswer.java

for (Blog blog : posts) {
      allAuthors.addAll(posts.getAllAuthors());
    }

Well first off posts doesnt even exist. I think you perhaps meant to say mPosts as that is the instance variable of our class that holds the BlogPost objects. Secondly, look at this:

List<BlogPost> mPosts

Our mPosts value is a list of BlogPost objects and not a Blog object. Also there is no property in the Blog class that holds the author names. There is also no such method called getAllAuthors() aside from the the current method we are working on. What you want is to run the getAuthor() method which grabs the author name of our BlogPost object. We also are only adding one string to our set per loop so the addAll method wont work.

Here is the actual answer which I will go into detail:

answer.java

public Set<String> getAllAuthors() { //this will return a set of strings
    Set<String> allAuthors= new TreeSet<>(); //initialize a treeset
    for (BlogPost post : mPosts) { // loop through each BlogPost object in our mPosts list
     allAuthors.add(post.getAuthor()); //each time we loop, call the getAuthor() method on our BlogPost which grabs the 
                                                           //author. and then we can it to our set
    }
    return allAuthors; //return the set
  }

Kevin

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Yahya Saadi

Yahya Saadi

SETS. Am doing something wrong, please help.

1 Answer

Kevin Faust

Kevin Faust

Yahya Saadi

Yahya Saadi