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

Posted by Unsubscribed User
Unsubscribed User
1,118 Points

Cannot figure out why I am getting a java.lang.reflect.InvocationTargetException error? Please help.

This code below ran fine until I added the last method getCategoryCount() method in Blog.java below.

After coding this method, I began getting a java.lang.reflect.invocationTargetException error. I do not know why and how to move past this. Please help.

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 nPost: mPosts) {
      authors.add(nPost.getAuthor());
    }
    return authors;
  }

 public Map <String,Integer> getCategoryCounts(){
    Map <String, Integer> CatCount = new HashMap<String, Integer>();
    for (BlogPost post: mPosts){
        //go to each BlogPost, get the category and insert into the Map
      String Category = post.getCategory();
      Integer Count  = CatCount.get(Category); 
      if (Count ==0){
           Count = 0;
         }
      Count ++;
      CatCount.put(Category, Count);  
      }
    return CatCount;
     }

}
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 nPost: mPosts) {
      authors.add(nPost.getAuthor());
    }
    return authors;
  }

 public Map <String,Integer> getCategoryCounts(){
    Map <String, Integer> CatCount = new HashMap<String, Integer>();
    for (BlogPost post: mPosts){
        //go to each BlogPost, get the category and insert into the Map
      String Category = post.getCategory();
      Integer Count  = CatCount.get(Category); 
      if (Count ==0){
           Count = 0;
         }
      Count ++;
      CatCount.put(Category, Count);  
      }
    return CatCount;
     }

}

2 Answers

Seth Kroger
Seth Kroger
56,413 Points
Seth Kroger
Seth Kroger
56,413 Points

The issue is here:

      Integer Count  = CatCount.get(Category); 
      if (Count ==0){
           Count = 0;
         }

It doesn't make much sense to assign count to zero if it's already zero. However you can get a null for Count and you should be checking for that.

      Integer Count  = CatCount.get(Category); 
      if (Count == null){
           Count = 0;
      }
Unsubscribed User
Unsubscribed User
1,118 Points
Unsubscribed User
Unsubscribed User
1,118 Points

.... and there it was.

No idea why I was checking for Count ==0, and not null. Goes to show that I should probably get some sleep now. Thanks Seth.