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

Posted by shaunsmith
shaunsmith
12,145 Points

I'm not sure how to finish the getCatagoryCount method?

I tried to follow the video examples, but I think I'm a little lost.

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 Map<String, Integer> getCategoryCounts(){
    Map<String, Integer> count = new HashMap<String, Integer>();
    for(BlogPost post : BlogPost){
      for(string cat : BlogPost.getCatagory()){
        Integer count = (cat);
        count = 0;
      }
      count++;
      hashTagCount.put(hasTag, count);


  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.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;
  }
}
Olga Ivancic
Olga Ivancic
8,137 Points
Olga Ivancic
Olga Ivancic
8,137 Points

You only need one "for" loop because in the video Craig has multiple hash tags in one treet. But in the BlogPost case there is only one category per each post. Here is the code:

    public Map<String, Integer> getCategoryCounts() {
    Map<String, Integer> categoryCount = new HashMap<String, Integer>();

    for(BlogPost post : mPosts) {
      String category = post.getCategory();
      Integer count = categoryCount.get(category);
      if (count == null) {
        count = 0;
      }
      count++;
      categoryCount.put(category, count);
    }
    return categoryCount;
  }

2 Answers

Simon Coates
Simon Coates
28,694 Points
Simon Coates
Simon Coates
28,694 Points

The following seems to work, though i needed some additional import statements for Map, HashMap (which should be in java.util)

   public Map<String, Integer> getCategoryCounts()
    {
        Map<String, Integer> catToCount = new HashMap<String, Integer>();
        for(BlogPost post : mPosts)
        {
            String cat =  post.getCategory();
                Integer count = catToCount.get(cat);
              if(count==null) catToCount.put(cat, 1);
              else {
                catToCount.put(cat, count+1);
              }
        }
        return catToCount;
    }

(oops, i didn't notice Olga Ivancic's response when i first submitted.)

Olga Ivancic
Olga Ivancic
8,137 Points
Olga Ivancic
Olga Ivancic
8,137 Points

I'm glad you posted your version. I like your approach better - less code :) Thanks for sharing!

shaunsmith
shaunsmith
12,145 Points
shaunsmith
shaunsmith
12,145 Points

Thank you both! It worked great, and I understand a little better!