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Java Java Data Structures Exploring the Java Collection Framework Maps

James N
James N
17,864 Points
Posted by James N
James N
17,864 Points

They tell me to loop over all the posts...

But, what they don't tell me is what the variable with all the posts is called! :'(

Thanks for your help!

My BlogPost.java code:

com/example/BlogPost.java 
package com.example;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Map;
import java.util.HashMap;


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;
  }

  public Map<String, List<BlogPost>> getCategoryCouts() {
    Map<String, List<BlogPost>> BlogPostsByCategory = new HashMap<String, List<BlogPost>>();
    for (BlogPost post : blogPosts) {
      List<BlogPost> CategorizedBPs = BlogPostsByCategory.get(post.getCategory());
        if (CategorizedBPs == null) {
          CategorizedBPs = new ArrayList<BlogPost>();
          BlogPostsByCategory.put(post.getCategory(), CategorizedBPs);

        }
      CategorizedBPs.add(post);
    }
  }
}

My Blog.java code:

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;
  }
}

1 Answer

Jennifer Nordell
seal-mask
STAFF
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher
Jennifer Nordell
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher

Hi there! Sure they do! Take a look at this line:

List<BlogPost> mPosts;

This is a list of of type BlogPost. Hope this helps! :sparkles:

James N
James N
17,864 Points
James N
James N
17,864 Points

Oh. in the blog class. (-_Q) duh. Thanks for your help! forgot to put the code in the blog class.......

James N
James N
17,864 Points
James N
James N
17,864 Points

I still have a problem with the code, however. even after moving it to the blog class, i get the following message directly from that top bar:

Bummer! Uh oh. java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl cannot be cast to java.lang.Class

UPDATED CODE; BLOG.JAVA

Blog.java 
package com.example;

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

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, List<BlogPost>> getCategoryCounts() {
    Map<String, List<BlogPost>> BlogPostsByCategory = new HashMap<String, List<BlogPost>>();
    for (BlogPost post : mPosts) {
      List<BlogPost> CategorizedBPs = BlogPostsByCategory.get(post.getCategory());
        if (CategorizedBPs == null) {
          CategorizedBPs = new ArrayList<BlogPost>();
          BlogPostsByCategory.put(post.getCategory(), CategorizedBPs);

        }
      CategorizedBPs.add(post);
    }
    return BlogPostsByCategory;
  }
}

MY UPDATED CODE; BLOGPOST.JAVA

BlogPost.java 
package com.example;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Map;
import java.util.HashMap;


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;
  }


}