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

luis martinez
luis martinez
2,480 Points
Posted by luis martinez
luis martinez
2,480 Points

getCategoryCounts

package com.example;

import java.util.ArrayList;
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 Category : post.getWords())//It tells me expected 1 but returns null
      {
        Integer count = CategoryCounts.get(Category);
        if (count == null)
        {
          count = 0;
        }
        count ++;
        CategoryCounts.put(Category, count);
      }
    }
   return CategoryCounts; 
  }
}

[MOD: added ```java markdown formatting -cf]

2 Answers

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,441 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points

Your code is very close. There isn't a need to look at the words within each BlogPost. Only the BlogPost Category is needed.

  public Map<String, Integer> getCategoryCounts()
  {
    Map<String, Integer> CategoryCounts = new HashMap<String, Integer>();
    for (BlogPost post : mPosts)
    {
      // removed for-loop
      // for (String Category : post.getWords())//It tells me expected 1 but returns null
      // {
        Integer count = CategoryCounts.get(post.getCategory());  // <-- get current count of current post's category
        if (count == null)
        {
          count = 0;
        }
        count ++;
        CategoryCounts.put(post.getCategory(), count);  // <-- update count of current post's category
      // }
    }
   return CategoryCounts; 
  }
Grigorij Schleifer
Grigorij Schleifer
10,365 Points
Grigorij Schleifer
Grigorij Schleifer
10,365 Points

Hi luis,

public Map<String, Integer> getCategoryCounts() {
    // create a Map that accepts a String as key and an Integer as value
    // so the key is the category
   // and value is the count how many categories are in the post
    Map<String, Integer> categoryCount = new HashMap<String, Integer>();

    // loop over every post in mPosts
    for(BlogPost post: mPosts) {
      String category = post.getCategory();
        // No need to create a second/nested for loop
        // create new count and proof whether a category in there using getCategory()
        // getCategory returns a null if no category is in the post
        // increment if getCategory returns not null (post is not empty)
        Integer count = categoryCount.get(category);
          if(count == null) {
            count = 0;
          }
        count++;
        // put category as key and count as value in Map
        categoryCount.put(category, count);
      }
     return categoryCount;
    }

Let me know if you need more help

Grigorij