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

Posted by Alexander Walley
Alexander Walley
3,180 Points

How do I get all of the authors names? sets 2

I understand how to make the set, and it should be a TreeSet, but how do I get all of the authors names to sort through?

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.Set;
import java.util.TreeSet;

import java.util.List;

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 = TreeSet<String>();
    for(String author : BlogPost.getAuthor()){
     allAuthors.add(author); 
    }
  }
  return allAuthors;
}

1 Answer

Kourosh Raeen
Kourosh Raeen
23,733 Points
Kourosh Raeen
Kourosh Raeen
23,733 Points

There are several issues:

1) When creating the TreeSet you need to use the new operator.

2) The return statement should be inside the method.

3) BlogPost.getAuthor() would not work since it is not a static method of the class. You need to call it on an instance of the BlogPost class. Since you have all instances of BlogPost in the member variable mPosts you can loop over that and then call getAuthor() on each instance:

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