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

Ashish Soni
Ashish Soni
2,320 Points

Map Objective

return map of category to count calculated by looping on all posts

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.List;
import java.util.Map;
import java.util.Set;
import java.util.HashMap;
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> map = new HashMap<String ,Integer>();
    for(BlogPost post : getAllAuthors()) {

    }
  }
}

1 Answer

Simon Coates
Simon Coates
28,694 Points

For starters, you need to iterate over mPosts. The following seems to work:

package com.example;

import java.util.List;
import java.util.Set;
import java.util.TreeSet;
//new imports
import java.util.Map;
import java.util.HashMap;

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> map = new HashMap<String ,Integer>();
    for(BlogPost post : mPosts) {
        //retrieve Integer value out of map for post.getCategory()
        Integer count = map.get(post.getCategory());
        //if no value, set to 0.
        if(count == null) {
          count = 0;
        }
        count += 1;

        //put updated integer back into map.
        map.put(post.getCategory(), count);
    }
    return map;
  }

}
Ashish Soni
Ashish Soni
2,320 Points

Hi Simon Coates, Thanks a lot for your solution.