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

Posted by Kyler Callaway
Kyler Callaway
6,257 Points

How do I solve this?

I am new to the Maps Interface and generics in general can someone please explain this to me ?

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

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> getCategoryCount<String>(){
    Map<String,Integer> CategoryCount = new HashMap<String,Integer>();
    for(BlogPost blog : mPosts){
      Integer counts = CategoryCounts.get(blog);
      if(count ==null){
        count =0;
      }
      count++;
      getCategoryConts.put(blog,counts);
}
    return CategoryCount;
  }
}

2 Answers

jcorum
jcorum
71,830 Points
jcorum
jcorum
71,830 Points

Grigorij has covered it well! But if you want another take on it here's a link to a slightly different line-by-line explanation: https://teamtreehouse.com/community/java-help-7

Grigorij Schleifer
Grigorij Schleifer
10,365 Points
Grigorij Schleifer
Grigorij Schleifer
10,365 Points

Hey jcorum you are absolutely right !

Ken Alger for president !!!

Oh no I forget, Craig is already nominated :)))

Grigorij Schleifer
Grigorij Schleifer
10,365 Points
Grigorij Schleifer
Grigorij Schleifer
10,365 Points

Hey Kyler,

you are very close:

  public Map<String, Integer> getCategoryCounts() { // <String> deleted, <Integer> added
    Map<String, Integer> CategoryCount = new HashMap<String, Integer>();
    for (BlogPost blog : mPosts){
        Integer count = CategoryCount.get(blog.getCategory());  
     // specify what you need from the "blog" using getCategory() method
     // count the returned categories 
        if (count == null){
          count = 0;
     // if no category yet, getCategory() will return null
     // set the count to 0 if no categories yet
        }
        count ++;
      // increase the count if Category is found
        CategoryCounts.put(blog.getCategory(), count);  
     // put the caregory as key and the number as value into the Map
    }
   return CategoryCounts; 
     // and return it
}

Makes sense?

Grigorij