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

Chris Needham
Chris Needham
1,871 Points

Not sure why this answer is wrong, the error says I'm returning what the instructions said to return.

Not sure why this answer is wrong, the error says I'm returning what the instructions said to return.

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.*;

public class Blog {
  List<BlogPost> mPosts;

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

  public List<BlogPost> getPosts() {
    return mPosts;
  }

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

}

1 Answer

andren
andren
28,558 Points

The error states that you should return Set<String>, but are returning Set, which is technically not the same thing.

The issue is that you have not specified the type of Set in the return type of the method. If you add <String> to the return type like this:

public Set<String> getAllAuthors() // Added <String> to return type
{
  Set<String> authors = new TreeSet<String>(); 
  for(BlogPost post : mPosts )
  {
    authors.add(post.getAuthor()); 
  }
  return authors; 
}

Then your code will work.