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

CHIRAG SARAOGI
CHIRAG SARAOGI
1,280 Points
Posted by CHIRAG SARAOGI
CHIRAG SARAOGI
1,280 Points

Getting error on getAuthor() and mPost.

Questions/Uncertainity I have are:

  1. I have created a set of strings because getAuthor returns strings
  2. using a post loop because we want to access the authors of all the post from BlogPost
  3. how to call the function in BlogPost call from another class
  4. returning the set of strings called authors
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 com.example.BlogPost;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;
import java.util.HashSet;

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> authors = new TreeSet<String>(); 
    for( String authorresult : mPosts.getAuthor())
    {
     authors.addAll(authorresult);
    }

    return authors;

  }
}

1 Answer

Kiran Kumar Devarasetty
Kiran Kumar Devarasetty
3,047 Points
Kiran Kumar Devarasetty
Kiran Kumar Devarasetty
3,047 Points

for( String authorresult : mPosts.getAuthor())

First problem is mPosts is a List and it does not have the method getAuthor(). getAuthor() is a method in BlogPost.

Second problem is in the usage of the "for" construct. This form of "for" should be used on a Collection(such as List) where it is possible to iterate over each element.

The correct usage is for( BlogPost bPost : mPosts) {}

and then you can add the author of each bPost (returned by the iterator) to the authors Set. See below:

for( BlogPost bPost : mPosts) { authors.add(bPost.getAuthor()); }