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

Posted by mos per
mos per
Courses Plus Student 1,172 Points

why am i getting this error?

i think i got it right. but im getting this annoying error:

" ./com/example/Blog.java:24: error: for-each not applicable to expression type for(String category : post.getCategory()){ ^ required: array or java.lang.Iterable found: String " somebody please help.

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.*;
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  Map <String, Integer> getCategoryCounts()
  {
        Map <String, Integer> categoryCount = new HashMap <String, Integer>();


      for (BlogPost post: mPosts) {
       for(String category : post.getCategory()){

        Integer count = categoryCount.get(category);
          if (count == null) {
           count = 0;
          }
         count++;

         categoryCount.put(category, count);
        }

         System.out.println("category count" + categoryCount);  
        }


    }



  public Set<String> getAllAuthors() {
    Set<String> authors = new TreeSet<>();
    for (BlogPost post: mPosts) {
      authors.add(post.getAuthor());
    }
    return authors;
  }
}

1 Answer

Grigorij Schleifer
Grigorij Schleifer
10,365 Points
Grigorij Schleifer
Grigorij Schleifer
10,365 Points

Hi mos,

lets take a look at your code:

    public  Map <String, Integer> getCategoryCounts(){
        Map <String, Integer> categoryCount = new HashMap <String, Integer>();
   // create a loop that loops over every post inside mPosts
   // every post has a category, so you can count the number of categories 

      for (BlogPost post: mPosts) {
     // so every "post" is equals one categry
     // for(String category : post.getCategory()){
     // no need for the second for-loop

      Integer count = categoryCount.get(post.getCategory());
    // create an integer to store the number of categories
    // try to get the category out of your new Map
    // at the beginning there are no categories inside
    // getCategory will return null

       if (count == null) {
    // thats why set the count to 0
           count = 0;
          }
         count++;
   // next post inside the loop will check the second post
   // so increase the count
   // categoryCount.put(category, count); // deleted this line

    categoryCount.put(post.getCategory(), count);  
         // put the category as key and count as value into the Map
         // System.out.println("category count" + categoryCount);  
         // no need for printing the result
      }
  return categoryCount;
         // but dont forget to return the Map because the method has a Map return type
}

And don´t forget to import Map and HashMap !

Makes sense?

Grigorij

mos per
mos per
Courses Plus Student 1,172 Points

Ingenuity!

Thanx a ton!

Grigorij Schleifer
Grigorij Schleifer
10,365 Points
Grigorij Schleifer
Grigorij Schleifer
10,365 Points

:smiley:

Glad I coukd help !

See you in the forum mos !