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Elvin Roldan
1,473 PointsgetAllAuthors method - Java Data Structures
Cant seem to get this one right. The challenge asks for a method that produces a Set of Strings with the authors collected from the posts List. I created the Set and have the imports for the HashSet and implemented a for Structure to iterate through BlogPost mPosts to add the values to authors Set through posts in the parameters set in the for Structure.
If anyone can tell me how to decipher this I would really appreciated.
Thank You.
package com.example;
import java.util.List;
import java.util.HashSet;
import java.util.Set;
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 HashSet <String> ();
for (BlogPost posts : mPosts ){
authors.add(posts);
}
return authors;
}
[MOD: snipped code for brevity - srh]
3 Answers
Steve Hunter
57,712 PointsHi Elvin,
First off, you want to use a TreeSet as they sort more easily and the output wants a sorted output.
Second, you're trying to add the loop variable, posts - this is a BlogPost not a string. You want to call the getAuthor() method on posts to bring back the string of the author name.
Lastly, your braces aren't quite right - you seem to be missing one.
Those three changes, once you've amended your imports, should see you right.
Steve.
Felix Sonnenholzer
14,654 PointsHi Elvin,
it is almost right, but you are defining a Set of Strings but you are currently trying to store a BlogPost in your HashSet.
Furthermore the challenge wants you to return a alphabetically sorted set of authors (as Strings). So instead of a HashSet you should use a TreeSet since it sorts it automatically.
Also I think you are missing a closing }. It would look something like this:
public Set <String> getAllAuthors () {
Set <String> authors = new TreeSet<String> ();
for (BlogPost post : mPosts ) {
authors.add(post.getAuthor());
}
return authors;
}
Also don't forget to exchange the HashSet to a TreeSet in your imports
Elvin Roldan
1,473 Pointsthank you, that did it , previously I was calling the method as suggested to posts but wasn't applying a TreeSet I was applying the HashSet. What is the difference between the two?
Steve Hunter
57,712 PointsThe prime difference is that a TreeSet is automatically ordered by default. A HashSet is more memory/CPU efficient so, for large chunks of data, you'd add your items to a HashSet then switch to a TreeSet when you wanted the ordering functionality. But for what we're doing with them here, just use a TreeSet for the ordering requirement - we're not bothered about efficiency!
Those are the key differences.
Enjoy the rest of the course!
Steve.