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Java

Posted by Andrew Malia
Andrew Malia
2,616 Points

Java Sets Exercise

I am getting this error when trying to place all the authors into a TreeSet. 

./com/example/Blog.java:24: error: no suitable method found for addAll(String)
      allAuthors.addAll(post.getAuthor()); 
                ^
    method Collection.addAll(Collection) is not applicable
      (argument mismatch; String cannot be converted to Collection)
    method Set.addAll(Collection) is not applicable
      (argument mismatch; String cannot be converted to Collection)
Note: JavaTester.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
1 error

As far as I can tell this is telling me that I'm attempting to place a collection inside the TreeSet when I should be placing strings inside. But unless I'm missing something, I don't think post.getAuthor(); should return a collection. Any advice?

I've gone back and looked at the example Craig walked us through in my Workspace and to me, it looks functionally the same but obviously isn't.

Here is my code for Blog.java:

package com.example;

import java.util.List;
import java.util.HashSet;
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 Set<String> getAllAuthors() {
   Set<String> allAuthors = new TreeSet<String>();
   for (BlogPost post : mPosts) {
      allAuthors.addAll(post.getAuthor()); 
   }
   return allAuthors; 
  }
}

And my code for 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;
  }
}

1 Answer

Seth Kroger
Seth Kroger
56,416 Points

You're pretty close here with. There's a difference between the methods add() and addAll(). add() takes a single item, while addAll() adds multiple items in a collection, and only accepts a collection. Since posts only have one author in the Post class, you should use add() instead of addAll()

Andrew Malia
Andrew Malia
2,616 Points

This worked. Thanks Seth!