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Java Java Data Structures Exploring the Java Collection Framework Sets

Damjan Vlaic
Damjan Vlaic
19,244 Points
Posted by Damjan Vlaic
Damjan Vlaic
19,244 Points

---JAVA---

I don't know where did i made a mistake here. Can someone help pls ;)

I've added a new class called Blog. It is initialized with a list of BlogPost objects. Create a method in the Blog class called getAllAuthors that loops over all the posts and returns a java.util.Set of all the authors, which are stored as Strings. They should be sorted alphabetically.

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.HashSet;
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> allAuthors = new TreeSet<String>();
    for (BlogPost blogPost : posts) {
      allAuthors.addAll(blogPost.getAuthor());
    }
    return allAuthors;
  }
}

2 Answers

Yanuar Prakoso
Yanuar Prakoso
15,196 Points
Yanuar Prakoso
Yanuar Prakoso
15,196 Points

I try the challenge and pass it. This is the code I used to pass the challenge:

package com.example;

import java.util.List;
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> allAuthors = new TreeSet<>();
    for (BlogPost blogPost : mPosts) {
      allAuthors.add(blogPost.getAuthor());
    }
    return allAuthors;
  }
}

Can you tell me what kind of error you are having?

Damjan Vlaic
Damjan Vlaic
19,244 Points
Damjan Vlaic
Damjan Vlaic
19,244 Points

ahha i didn't write for loop correctly like you did, now everythins is working, tnx man ;)

Yanuar Prakoso
Yanuar Prakoso
15,196 Points
Yanuar Prakoso
Yanuar Prakoso
15,196 Points

Hi There...

The problem is in your getAllAuthor method, as shown here:

 public Set<String> getAllAuthors() {
    Set<String> allAuthors = new TreeSet<String>();
    for (BlogPost blogPost : posts) { //<-- this should be mPost not post
      allAuthors.addAll(blogPost.getAuthor());//<-- change this to: allAuthors.add(blogPost.getAuthor), do not use addAll
    }
    return allAuthors;
  }

I hope that can help you a little

Damjan Vlaic
Damjan Vlaic
19,244 Points
Damjan Vlaic
Damjan Vlaic
19,244 Points

it still gives me an error but tnx for helping ;)