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Java Java Data Structures Exploring the Java Collection Framework Maps

Steven Morimoto
PLUS
Steven Morimoto
Courses Plus Student 1,836 Points
Posted by Steven Morimoto
Steven Morimoto
Courses Plus Student 1,836 Points

Please help. I do not get the Maps quiz

Hi, i have narrowed down all of the errors to just one. The problem is line 33 of Blog class is basically the same as it was in the getAllAuthors() method above, since you can access BlogPost methods. But line 33 is apparently in error and I don't know why. Some assistance would be appreciated.

Thank you,

Steve

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 com.example.BlogPost;
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 Set<String> getAllAuthors() {
    Set<String> authors = new TreeSet<>();
    for (BlogPost post: mPosts) {
      authors.add(post.getAuthor());
    }
    return authors;
  }
  public Map<String, Integer> getCategoryCounts()
  {
    Map<String, Integer> categoryCounts = new HashMap<String, Integer>();
    for(BlogPost post : mPosts)
    {
      for(String categoryFound : post.getCategory())
      {
        Integer count = categoryCounts.get(categoryFound);
        if(count == null)
        {
          count = 0;
        }
        count++;
        categoryCounts.put(categoryFound, count);
      }
    }
    return categoryCounts;
  }


}

2 Answers

andren
andren
28,558 Points
andren
andren
28,558 Points

The issue is that the post.getCategory() method returns a category, a single one. Not a list of categories. Therefore it can't be looped through.

That's not really an issue though, because it doesn't need to be looped through. Since it's just a single regular String you can just assign it to a variable without a loop like this:

public Map<String, Integer> getCategoryCounts()
  {
    Map<String, Integer> categoryCounts = new HashMap<String, Integer>();
    for(BlogPost post : mPosts)
    {
        // Removed for loop
        String categoryFound = post.getCategory(); // Assign the category to a variable normally
        Integer count = categoryCounts.get(categoryFound);
        if(count == null)
        {
          count = 0;
        }
        count++;
        categoryCounts.put(categoryFound, count);
    }
    return categoryCounts;
  }

Then your code will work perfectly fine.