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

Elvin Roldan
Elvin Roldan
1,473 Points

getCategoryCounts

Hello:

I'm trying to resolve this HashMap exercise I tried the nested iteration to get the counts for categories within posts but I get an error in "error 31" as if some parameter is missing in the getCategory method use in the iteration.

if someone can check m,y code to resolve this exercise I would really appreciated. Thank You.

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;
import java.util.HashMap;
import java.util.Map;

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> categoryCount = new HashMap <String, Integer> (); //Creation of Map Object 
    for (BlogPost posts : mPosts){  //Iteration through posts in BLogPost 
      for (String cat : posts.getCategory()){  //Nested iteration to get Categories in Posts
        Integer count = categoryCount.get(cat); // count for repetition of category using  cat object
        if  (count == null){ //parameter for setting count to 0 if "count" == null
          count = 0;
        }
        count++; // adding counter for repetiotion of category within posts
        categoryCounts.put(cat, count); //adding cat and counter to HashMap
      }
      return categoryCount; // returns HashMap reults
    }
  }
}

1 Answer

Brin Colnar
Brin Colnar
3,755 Points

This line here is the problem:

for (String cat : posts.getCategory()){...}

posts.getCategory() returns a String; if you want to loop through all categories you should create a list of type String and then String cat can loop through the list you created. Remember to import ArrayList. Like this:

public Map<String, Integer> getCategoryCounts {
  Map <String, Integer> catCount = new HashMap<String, Integer>();
  List<String> catList = new ArrayList<String>;//creating a list that will hold categories

  for(BlogPost post : mPosts) {
    catList.add(post.getCategory()); //filling the list 
  }
  //notice that for loops aren't nested
  for(String cat : catList) {
  //blah-blah
  }
}