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

Deano k
PLUS
Deano k
Courses Plus Student 5,872 Points
Posted by Deano k
Deano k
Courses Plus Student 5,872 Points

What's wrong with my code?

getting an InvocationTargetException error message.. :/ What did I do wrong?

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.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> catCount = new HashMap<String, Integer>();
    for (BlogPost post : mPosts) {
       Integer count = catCount.get(post.getCategory());
       if (count == 0) {
         count = 0;
       }
       count++;
       catCount.put(post.getCategory(),count);
    }
    return catCount;
  }
}

1 Answer

Jeremy Hill
Jeremy Hill
29,567 Points
Jeremy Hill
Jeremy Hill
29,567 Points

Here is the code that worked for me:

public Map<String, Integer> getCategoryCounts(){

    Map<String, Integer> categoryCounts = new TreeMap<>();
    Integer count = 0;

    for(BlogPost post: mPosts){
      count = 0;
      for(BlogPost bp: mPosts){  // I used a nested for loop here to count all of the like categories for each element.
         if(post.getCategory() == bp.getCategory()){
           count++;
         }
      }
      categoryCounts.put(post.getCategory(), count); // after the inner loop ends I added the current element of the outer loop to the map.
    }

    return categoryCounts;  
  }