Help with Challenge error - "for-each not applicable to expression type | require Array or List"

Question

I think i'm close to the solution but I'm having trouble with my nested for loop. In the second for loop im trying to iterate from category to getCategory but i'm not passing an array or list

if I'm thinking about the solution incorrectly please also let me know!

package com.example;

import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeSet;

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<>();
    for (BlogPost post: mPosts) {
      authors.add(post.getAuthor());
    }
    return authors;
  }

  public Map<String,Integer> getCategoryCounts() { 
    Map<String,Integer> categoryCounts = new HashMap<String,Integer>();
    //categoriedPost = new ArrayList<BlogPost>();   
    for (BlogPost post : mPosts) {
      for (String category : post.getCategory()) { //How do I iterate over categories?
        Integer count = categoryCounts.get(category);
        if (count == null) {
          count = 0; 
        }
        count++;
        categoryCounts.put(category,count);
      }
    }

}

Answer 1 · 2016-12-01T03:48:34Z

December 1, 2016 3:48am

Each post has a single category if you look at the BlogPost source code. So you've trying to loop on something that can't be looped on.

  public Map<String,Integer> getCategoryCounts() { 
    Map<String,Integer> categoryCounts = new HashMap<String,Integer>();
    //categoriedPost = new ArrayList<BlogPost>();   
    for (BlogPost post : mPosts) {
      String category = post.getCategory();
      Integer count = categoryCounts.get(category);
      if (count == null) {
        count = 0; 
      }
      count++;
      categoryCounts.put(category,count);
    }
    return categoryCounts ;
  }

this is a very common mistake that people seem to make. not sure if it's because people assume there should be multiple categories or if its a function of confusion over the for loop. If you read the colon in the for loop as 'in', then it should be clear that the syntax is only for collections. Apart from this, your code was missing a return statement.

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Colby Wise

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Help with Challenge error - "for-each not applicable to expression type | require Array or List"

1 Answer

Simon Coates

Simon Coates