Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

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

Iain Diamond
Iain Diamond
29,379 Points

Maps Challenge

When I run 'Check Work' it tells me I'm returning the wrong count for food, 'expected 2, received 3'. However, I've rewritten the code out in full externally with my own tests and I can't recreate the problem. Any clues are most welcome.

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;
  }
}

Blog.java

package com.example;

import java.util.HashMap;
import java.util.List;
import java.util.Map;
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 Map<String, Integer> getCategoryCounts() {
    Map<String, Integer> categoryCounts = new HashMap<>();
    Integer count = 0;

    for (BlogPost post: mPosts) {
      String category = post.getCategory();

      // Check if the category is new
      if (!categoryCounts.containsKey(category)) {
        count = 0;
      }
      count++;
      categoryCounts.put(category, count);
    }
    return categoryCounts;
  }

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

1 Answer

Craig Dennis
STAFF
Craig Dennis
Treehouse Teacher

Hmmm...what if that count variable was inside the for loop? Seems to be ever incrementing and not resetting. In fact, what if you got it out of the Map each time by key. Remember if a key doesn't exist you will get back a null value.

That help? (I can be less hinty if you want me to be) ;)

Iain Diamond
Iain Diamond
29,379 Points

Hi Craig, I'll mull over your clue.

Just for the record I've included my test case and the results below. I'm very puzzled as the results are telling me the counter is working properly.

public class myTreehouseREPL {

  public static void main(String... args) {
    List<BlogPost> blogPosts = new ArrayList<>();

    BlogPost post1 = new BlogPost("blogscot", "Learning Java", "Hey, I'm learning how to program Java using Treehouse!", "Python", new Date(1434015393));
    BlogPost post4 = new BlogPost("kosh", "Learning Java", "Hey, I'm learning how to program Java using Treehouse!", "JavaScript", new Date(1434015393));
    BlogPost post2 = new BlogPost("kosh", "Learning Java", "Hey, I'm learning how to program Java using Treehouse!", "Python", new Date(1434015393));
    BlogPost post5 = new BlogPost("kosh", "Learning Java", "Hey, I'm learning how to program Java using Treehouse!", "JavaScript", new Date(1434015393));
    BlogPost post6 = new BlogPost("G'kar", "Learning Java", "Hey, I'm learning how to program Java using Treehouse!", "Java", new Date(1434015393));
    BlogPost post10 = new BlogPost("kosh", "Learning Java", "Hey, I'm learning how to program Java using Treehouse!", "PHP", new Date(1434015393));
    BlogPost post7 = new BlogPost("Delenn", "Learning Java", "Hey, I'm learning how to program Java using Treehouse!", "Java", new Date(1434015393));
    BlogPost post8 = new BlogPost("kosh", "Learning Java", "Hey, I'm learning how to program Java using Treehouse!", "Java", new Date(1434015393));
    BlogPost post3 = new BlogPost("kosh", "Learning Java", "Hey, I'm learning how to program Java using Treehouse!", "JavaScript", new Date(1434015393));
    BlogPost post9 = new BlogPost("Garabaldi", "Learning Java", "Hey, I'm learning how to program Java using Treehouse!", "Java", new Date(1434015393));

    List<BlogPost> posts = Arrays.asList(post1, post2, post3, post4,post5,post6,post7,post8,post9,post10);

    Blog blog = new Blog(posts);
    Set<String> authors = blog.getAllAuthors();
    authors.forEach(System.out::println);

    Map<String, Integer> categories = blog.getCategoryCounts();
    for(Map.Entry entry: categories.entrySet()) {
      System.out.printf("category %s: count:%d%n", entry.getKey(), entry.getValue());
    }
  }

And here are the results.

Delenn
G'kar
Garabaldi
blogscot
kosh
category Java: count:4
category JavaScript: count:3
category PHP: count:1
category Python: count:2
Craig Dennis
Craig Dennis
Treehouse Teacher

Hmm...try making those numbers a little less standard...add a PHP and a JavaScript.

Iain Diamond
Iain Diamond
29,379 Points

Thanks Craig, once I modified the posts I was able to figure out what I was doing wrong. Fixed it now. :)

Craig Dennis
Craig Dennis
Treehouse Teacher

Awesome way to stick with it! Crazy luck that was working, nothing worse than false positives. Congrats!