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Java Java Data Structures Exploring the Java Collection Framework Maps

David Sampimon
David Sampimon
12,026 Points
Posted by David Sampimon
David Sampimon
12,026 Points

What am I doing wrong? Bummer! Yikes, java.lang.reflect.InvocationTargetException

Below is the code I created for this excersize (the getCategoryCounts method in Blog.java). When I try to compile I get the "Bummer! Yikes, java.lang.reflect.InvocationTargetException" exception without further details.

What did I do wrong to get this exception?

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.HashMap;
import java.util.Map;
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;
  }


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

}

3 Answers

David Sampimon
David Sampimon
12,026 Points
David Sampimon
David Sampimon
12,026 Points

Found it!

line 34 in Blog.java

if ( count == 0) {

should have been

if ( count == null) {
Siu KWAN Yuen
PLUS
Siu KWAN Yuen
Courses Plus Student 2,898 Points
Siu KWAN Yuen
Siu KWAN Yuen
Courses Plus Student 2,898 Points

I encounter the same problem in part 1 of the exercise (getExternalLinks). I don;t know what "java.lang.reflect.InvocationTargetException" means and I can't really solve it. I will copy your code to pass the exercise, but I will post my solution below.

Siu KWAN Yuen
PLUS
Siu KWAN Yuen
Courses Plus Student 2,898 Points
Siu KWAN Yuen
Siu KWAN Yuen
Courses Plus Student 2,898 Points 
package com.example;

import java.io.Serializable;
import java.util.Date;
import java.util.List; 
import java.util.Arrays;
import java.lang.*; 

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 List <String> getExternalLinks() { 
    String[] myWord = getWords();
    List<String> myList = Arrays.asList(myWord); 
    for(String elem : myList) {
      if (!elem.startsWith("http")) {
        myList.remove(elem);
      }
    }
    return myList; 
  }

  public String[] getWords() {
    return mBody.split("\\s+");
  }

  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;
  }
}