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Java Java Data Structures Exploring the Java Collection Framework Maps

Jack Cummins
Jack Cummins
17,417 Points
Posted by Jack Cummins
Jack Cummins
17,417 Points

Why am I wrong. I do not get this.

Assessment: In Blog.java add a new method called getCategoryCounts. It should return a Map of category-to-count calculated by looping over all the posts.

com/example/BlogPost.java 
package com.example;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Map;
import java.util.HashMap;

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;
  }

    public Map<String, Integer> getCategoryCounts() {
    Map<String, Integer> categoryCounts = new HashMap<String, Integer>();
    for (BlogPost post : mPosts) {
        String category = post.getCategory();
        Integer count = categoryCounts.get(category);
        if (count == null) {
          count = 0;
        }
        count++;
        categoryCounts.put(category, count);
    }
    return categoryCounts;
  }
}
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

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

There are two files in this challenge, BlogPost.java and Blog.java (You can switch between them using the tabs above the coding area). The challenge asks you to add the getCategoryCounts method to Blog.java, but you have placed it in BlogPost.java instead.

The method you have written is perfectly fine, so if you simply move it (and the import statements) into Blog.java like this:

Blog.java

package com.example;

import java.util.List;
import java.util.Set;
import java.util.TreeSet;
import java.util.Map;
import java.util.HashMap;

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) {
        String category = post.getCategory();
        Integer count = categoryCounts.get(category);
        if (count == null) {
          count = 0;
        }
        count++;
        categoryCounts.put(category, count);
    }
    return categoryCounts;
  }
}

Then you will be able to pass the challenge.