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

Posted by Gabriel E
Gabriel E
8,916 Points

How do I create a getAllAuthors method?

Hello,

On this challenge, I need to gather all the blogs, and order the authors alphabetically. I tried matching some of my code to it, but I don't quite understand how to do it. Could you please help? Thanks!

com/example/BlogPost.java 
package com.example;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;


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;

public class Blog {
  Set<String> allAuthors = new TreeSet<String>();
  allAuthors.addAll(blog.getAllAuthors());


  List<BlogPost> mPosts;

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

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

1 Answer

Kristian Terziev
Kristian Terziev
28,449 Points
Kristian Terziev
Kristian Terziev
28,449 Points

You create the needed method like that:

public Set<String> getAllAuthors() {

}

Then you need to loop through the posts with a foreach loop and save them in a Set. Therefore you need to create that set beforehand. You are also asked to make the set sorted, meaning you should use TreeSet:

Set<String> allAuthors = new TreeSet<String>(); 

for (BlogPost post : mPosts) {
  allAuthors.add(post.getAuthor());
}

return allAuthors;

Of course for all that to work, you'll have to import both Set and Treeset:

import java.util.Set; 
import java.util.TreeSet;
Gabriel E
Gabriel E
8,916 Points

Thanks, but I still get a syntax error, because it says an enum is expected. Not sure what to do about this.

Gabriel E
Gabriel E
8,916 Points

Thanks, but I still get a syntax error, because it says an enum is expected. Not sure what to do about this.

Kristian Terziev
Kristian Terziev
28,449 Points

Can you paste the error here, please?

Gabriel E
Gabriel E
8,916 Points

Thanks i got it now!

Gabriel E
Gabriel E
8,916 Points

Thanks i got it now!

Gabriel E
Gabriel E
8,916 Points

Thanks i got it now!

Gabriel E
Gabriel E
8,916 Points

Thanks i got it now!

Christian Lawrence
Christian Lawrence
3,941 Points
Christian Lawrence
Christian Lawrence
3,941 Points

Hello,

I was doing this but with Lists and ArrayLists, it failed as it wanted to return a String. Does the ArrayList move the value to another object?

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