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

Gabriele Zurla
PLUS
Gabriele Zurla
Courses Plus Student 6,942 Points
Posted by Gabriele Zurla
Gabriele Zurla
Courses Plus Student 6,942 Points

I'm getting mad

Got this error:

./com/example/Blog.java:20: error: for-each not applicable to expression type for (String category : post.getCategory()){ ^ required: array or java.lang.Iterable found: String Note: JavaTester.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details. 1 error

Here's my code: Blog.java: http://dpaste.com/0NFNNKW BlogPost.java: http://dpaste.com/29QC13W

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 com.example.BlogPost;

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

  }

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

2 Answers

rtholen
rtholen
Courses Plus Student 11,859 Points

"I am getting mad". Welcome to my world! :)

As defined, a BlogPost can only have one category. It's giving you an error because you are trying to loop over all the categories in a BlogPost with 

for (String category : post.getCategory())

The "for loop" is expecting some kind of Collection of categories, but is getting only a single String.

Gabriele Zurla
PLUS
Gabriele Zurla
Courses Plus Student 6,942 Points
Gabriele Zurla
Gabriele Zurla
Courses Plus Student 6,942 Points

Thanks, I've done it now!

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

This works.