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Java Java Data Structures Exploring the Java Collection Framework Maps

Danilo ANRIA
Danilo ANRIA
1,571 Points
Posted by Danilo ANRIA
Danilo ANRIA
1,571 Points

Need help on the Challenge Task

I am having problems figuring out this error.

./com/example/Blog.java:31: error: for-each not applicable to expression type for(String category: posts.getCategory()){ ^ required: array or java.lang.Iterable found: String Note: JavaTester.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details. 1 error

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

}
Danilo ANRIA
Danilo ANRIA
1,571 Points
Danilo ANRIA
Danilo ANRIA
1,571 Points

The error refers to this line of code in the Blog.java

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

1 Answer

Christopher Debove
PLUS
Christopher Debove
Courses Plus Student 18,373 Points
Christopher Debove
Christopher Debove
Courses Plus Student 18,373 Points

Your trying to use a for on a String.

posts is an instance of BlogPost and the method getCategory on BlogPost returns a String. You can only use for-each loop on iterable and string is not.

public Map<String, Integer>getCategoryCounts() {
    Map<String, Integer> categoryCounts = new HashMap<String, Integer>();

    for (BlogPost post: mPosts) { // Iterating on each post (i changed it to singular)
        String category: post.getCategory(); // Getting the category for the post
        Integer count = categoryCounts.get(category); // Getting the count for this category

        if (count == null) {
            count = 0;
        }
        count++;

        categoryCounts.put(category, count);
    }

    return categoryCounts;
}

It should work like this.