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

confusing

Showing Error on line 18

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;
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> set = new TreeSet<String>();
      set.addAll(getPosts());    //Showing Error Here
      return set;
  }
}
./com/example/Blog.java:16: error: cannot find symbol
   public Set getAllAuthors(){
          ^
  symbol:   class Set
  location: class Blog
./com/example/Blog.java:17: error: cannot find symbol
      Set set = new TreeSet();
      ^
  symbol:   class Set
  location: class Blog
./com/example/Blog.java:17: error: cannot find symbol
      Set set = new TreeSet();
                            ^
  symbol:   class TreeSet
  location: class Blog
Note: JavaTester.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
3 errors

1 Answer

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,441 Points

According to the error log it can not find symbols Set and Treeset. Have they been imported?

After running your code in the challenge, I get a different error trace:

./com/example/Blog.java:18: error: no suitable method found for addAll(List)
    set.addAll(getPosts());    //Showing Error Here
       ^
    method Collection.addAll(Collection) is not applicable
      (argument mismatch; List cannot be converted to Collection)
    method Set.addAll(Collection) is not applicable
      (argument mismatch; List cannot be converted to Collection)
Note: JavaTester.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
1 error

You are trying to use addAll() to add a List of BlogPosts to a Set of Strings. The challenge only wants the authors in the list.

Loop over the BlogPost List and add each author returned from post.getAuthor()

Yup,i imported

Rushabha Jain, you imported in BlogPost.java but you didn't import in Blog.java. You have to import in both Java files.