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Java Java Data Structures Exploring the Java Collection Framework Maps

CHIRAG SARAOGI
CHIRAG SARAOGI
1,280 Points

Error at getCategory function call inside the for loop.

I hope this logic is correct. I am getting one error at getCategory() function call. Please help me understand where am I going wrong.

Thanks a lot

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.Map;
import java.util.Set;
import java.util.TreeSet;
import java.util.HashMap;
import java.lang.Iterable;
import com.example.BlogPost;

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

2 Answers

Dan Johnson
Dan Johnson
40,532 Points

getCategory returns a String so there's nothing to iterate through. Instead of the inner for-in loop you can switch to assignment:

String hashTag = catPost.getCategory();
CHIRAG SARAOGI
CHIRAG SARAOGI
1,280 Points

I deleted the inner for loop and inserted the above code, got multiple errors. Please help me understand the code.

Thank you Chirag Saraogi

Dan Johnson
Dan Johnson
40,532 Points

If you can post your updated code I'll look over it again.

CHIRAG SARAOGI
CHIRAG SARAOGI
1,280 Points

public Map<String, Integer> getCategoryCounts() { Map<String, Integer> result= new HashMap<String, Integer>(); for( BlogPost catPost : mPosts) { String hashTag = catPost.getCategory(); } return result; }

Dan Johnson
Dan Johnson
40,532 Points

The logic inside the inner loop was fine, just the inner loop itself was unneeded. As an outline:

// For each blog post
for( BlogPost catPost : mPosts)
    {
       // Get the category
       String hashTag = catPost.getCategory();
       // Use the category as a key
       Integer count = result.get(hashTag);
       if (count == null)
       {
        count = 0; 
       }
        count++;
        result.put(hashTag, count);
    }