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Java Java Data Structures Exploring the Java Collection Framework Sets

Olha Markova
Olha Markova
2,050 Points
Posted by Olha Markova
Olha Markova
2,050 Points

can not find symbol error

I am trying to complete the challenge, but I get an error messagem that getAuthor() in my code can not be found. Where is my mistake?

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 com.example.BlogPost;
import java.util.List;
import java.util.ArrayList;

public class Blog {
  List<BlogPost> mPosts;

  public Blog(List<BlogPost> posts) {
    mPosts = posts;
  }

  public List<BlogPost> getPosts() {
    return mPosts;
  }
   private List<String> geAllAuthors (String authors){
  List<String> results = new ArrayList<String>();
    for (String author : getAuthor())

    return results;
  }
}

1 Answer

Gyorgy Andorka
Gyorgy Andorka
13,811 Points
Gyorgy Andorka
Gyorgy Andorka
13,811 Points

Hello, Olha!

  • getAllAuthors() should be public, else it cannot be used outside the Blog class
  • the challenge says we should return a Set, not a List
  • no parameters needed for this method
  • among the different Set implementations, we might use a TreeSet here (don't forget to import it), because it automatically orders the string elements alphabetically by default (if no special sorting order were defined for them), as it is required by the challenge description
  • We have to iterate through mPosts, and for all the posts, add the author's name to our newly created set - the author's name we can get by calling the .getAuthor() method on the post.
  • A for loop's syntax looks like: for (<create a variable here which will refer to the n-th item in the collection> : <the collection you'd like to iterate through from the first to last element>) { <do this stuff here inside the braces for every item> }

Try to finish it yourself, but here is the final solution for reference:

  public Set<String> getAllAuthors() {
    Set<String> allAuthors = new TreeSet<>();
    for (BlogPost post : mPosts) {      
      String author = post.getAuthor();
      allAuthors.add(author);      
    }
    return allAuthors;
  }