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Java Java Data Structures Exploring the Java Collection Framework Maps

Paramvir Singh
Paramvir Singh
1,517 Points
Posted by Paramvir Singh
Paramvir Singh
1,517 Points

for-each loop cannot be used here

I was using a nested for-each loop for Maps. Then I was using for-each loop for the String type but it said it cannot be done.

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;
import com.example.BlogPost;
import java.util.*;

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> map = new HashMap<String, Integer>();

    for ( BlogPost x : mPosts ) {

      for ( String y : x.getCategory() ) {
        Integer count = map.get(y);
        if ( count == null ) {
          count = 0;
        }
        count++;
        map.put(y, count);
      }
    }

    return map;
  }

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

2 Answers

andren
andren
28,558 Points
andren
andren
28,558 Points

The getCategory method returns a single String, not a list of strings. A String by itself is not iterable in Java.

A BlogPost can only have one category assigned to it, so no looping is required when it comes to categories. Just use the String getCategory returns directly like this:

public Map<String, Integer> getCategoryCounts () {
  Map<String, Integer> map = new HashMap<String, Integer>();

  for ( BlogPost x : mPosts ) {
    String y = x.getCategory(); // Assign the category to y
    Integer count = map.get(y);
    if ( count == null ) {
      count = 0;
    }
    count++;
    map.put(y, count);
  }
  return map;
}

And then your code will work.

Paramvir Singh
Paramvir Singh
1,517 Points
Paramvir Singh
Paramvir Singh
1,517 Points

oohhhh, that makes so much sense and I feel like a stupid.

Thanks a lot for your help,andren.