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

Matt Adams
Matt Adams
4,856 Points
Posted by Matt Adams
Matt Adams
4,856 Points

Keep getting incorrect category counts

I continue to get incorrect category counts. Here is my code:

package com.example;

import java.util.HashSet; 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>(); Set<String> categories = new TreeSet<>(); for (BlogPost post : mPosts) { categories.add(post.getCategory()); for (String category : categories) { Integer count = categoryCounts.get(category); if (count == null) { count = 0; } count++; categoryCounts.put(category, count); } } return categoryCounts; } }

I've tried a few different variations here, including un-nesting the second 'for' loop in the getCategoryCounts, and using a HashSet instead of a TreeSet for the 'categories' variable. Any advice?

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

1 Answer

Grigorij Schleifer
Grigorij Schleifer
10,365 Points
Grigorij Schleifer
Grigorij Schleifer
10,365 Points

Hi Matt,

here is a commented code suggestion:

public Map<String, Integer> getCategoryCounts() {
    Map<String, Integer> categoryCount = new HashMap<String, Integer>();
    // create a Map that accepts a String as key and an Integer as value
    // so the key is the category (as String)
   // and value is the count how many categories are in the post (as Integer)
  // no need to create an extra Set for categories

    for(BlogPost post: mPosts) {
    // loop over every post in mPosts (you got it right)
    // you can examen every post later 
    // no need for a second for loop

      String category = post.getCategory();
        // "extract" the category name and (store it into a String) from the post

        Integer count = categoryCount.get(category);
         // create new count Integer to store the number of categories
        // proof whether a category is avalable in your post using getCategory() method 
        // getCategory returns a null if no category avalable in the map

          if(count == null) {
        // so if count is null, there is no category in the Map yet
            count = 0;
      // set count to 0
          }
        count++;
         // increment if getCategory returns not null (there is a category in the map)

        categoryCount.put(category, count);
         // put category as key and count as value in Map
      }
     return categoryCount;
    }

I hope I could help a little bit.

Grigorij

Matt Adams
Matt Adams
4,856 Points
Matt Adams
Matt Adams
4,856 Points

This is fantastic, thanks for your help Grigorij!