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

jinhwa yoo
jinhwa yoo
10,042 Points

I got stuck

what 's wrong ??

Hi jinhwa,

What code are you trying?

2 Answers

Your method looks good but you forgot to import Map and HashMap

import java.util.Map;
import java.util.HashMap;
jinhwa yoo
jinhwa yoo
10,042 Points

In Blog.java add a new method called getCategoryCounts. It should return a Map of category to count calculated by looping over all the posts.

package com.example;

import java.util.List;
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>();
    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;
  }
}