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

Posted by Jakub Szczepanik
Jakub Szczepanik
10,194 Points

Hey this code doesn't run for me. All the time it's showing that I haven't done all the imports I should.

What should I add here? It's still showing me problems with imports.

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.TreeSet;

import com.example.BlogPost;

public class Blog {
  List<BlogPost> mPosts;

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

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

  public List<BlogPosts> getAllAuthors() {
    Set<String> allPosts = new TreeSet<String>();
     for(String word: getPosts()) {
      if(word.equals(mAuthor)) { 
        allPosts.getAuthor(word);
      }
    }
    return allPosts;
  }

}

1 Answer

Thomas Nilsen
Thomas Nilsen
14,957 Points
Thomas Nilsen
Thomas Nilsen
14,957 Points

Your version:

public List<BlogPosts> getAllAuthors() {
    Set<String> allPosts = new TreeSet<String>();
     for(String word: getPosts()) {
      if(word.equals(mAuthor)) { 
        allPosts.getAuthor(word);
      }
    }
    return allPosts;
  }

The following things needs changing:

  • The method should return a Set, not a List
  • In you for loop, you're looping over BlogPosts objects, but you write String
  • No need for a if-check, you're just supposed to loop over everything and add it to the Set

Here is the correct version

  public Set<String> getAllAuthors() {
    Set<String> allPosts = new TreeSet<String>();
     for(BlogPost bp: getPosts()) {
      allPosts.add(bp.getAuthor());
    }
    return allPosts;
  }
}