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Java Java Data Structures Exploring the Java Collection Framework Maps

Ashish Soni
Ashish Soni
2,320 Points
Posted by 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
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
Ashish Soni
Ashish Soni
2,320 Points

Hi Simon Coates, Thanks a lot for your solution.