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Java Java Data Structures Exploring the Java Collection Framework Maps

Eirin Joahna Pamela Gonzales
Eirin Joahna Pamela Gonzales
8,686 Points

I got an error: for-each not applicable to expression type

What does this mean?

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

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

2 Answers

Dan Johnson
Dan Johnson
40,532 Points

The String class is not an Iterable in Java so it can't be used in a for-each loop. In other standard libraries for other languages where strings are iterables this would generally have a for-each pull out each character individually which isn't what you'd want to deal with in this case anyways.

With the nested for-each out of the way we can grab the category like this instead:

// Grab from each Post
String category = post.getCategory();
Eirin Joahna Pamela Gonzales
Eirin Joahna Pamela Gonzales
8,686 Points

Thanks Dan! I already solved it! I removed the inner for loop then, I used that statement. Thanks! :)

Had the same issue, worked out for me as well.!! thanks