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

Juan Santiago
Juan Santiago
3,766 Points

I'm stuck in the final challenge :( (Compiler error: not applicable to expression type)

I get the following compiler error (among 3 more):

./com/example/Blog.java:31: error: for-each not applicable to expression type for(String category: post.getCategory()){ ^ required: array or java.lang.Iterable found: String


I'm really confused, I think that the String variable must be transformed to an array... HELP!

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

1 Answer

Craig Dennis
STAFF
Craig Dennis
Treehouse Teacher

The inner for each loop is not needed, getCategory() returns a String, and that should be your key.

Hope that helps!

Juan Santiago
Juan Santiago
3,766 Points

Thank you so much. That makes so much sense now hahaha. Let me congratulate you for your excellent work as a teacher. Greetings from Mexico :D

Broderic Crowe
Broderic Crowe
1,549 Points

Hey Craig, I stumbled across this forum post and was able to modify the code so it passed the challenge (see code below). But I don't understand something: the Integer "count" is set to "categoryCounts.get(category);" but how does this even register as a number? It's referencing its own Map (categoryCounts), and fetching a String! (category). How does this translate into an integer?

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);
      //how is this an integer? ^^^^^^^^^^^^^^^
      if (count == null) {
        count = 0;
      }
      count++;
      categoryCounts.put(category, count);
    }
    return categoryCounts;
  }

Any feedback would be awesome! Broderic