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

Albert Kirchmeyr
Albert Kirchmeyr
11,410 Points
Posted by Albert Kirchmeyr
Albert Kirchmeyr
11,410 Points

Can't get it - get a Compile error on addAll

Who can help me here?

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.*;


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.HashSet;
import java.util.Set;
import java.util.*;

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 post : mPosts) {
      allAuthors.addAll(post.getAuthor());
    }
  return allAuthors;
  }
}
Albert Kirchmeyr
Albert Kirchmeyr
11,410 Points
Albert Kirchmeyr
Albert Kirchmeyr
11,410 Points

I am hanging in there with allAuthors.addAll(post.getAuthor()); -> this gives an compile error instead of adding the author to the list....

1 Answer

andren
andren
28,558 Points
andren
andren
28,558 Points

The addAll method is used to add a collection of items to a set, not an individual item. To add an individual item you need to use the add method instead.

So by simply changing addAll to add like this:

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

Your code will pass.