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

Sara Pasinato
Sara Pasinato
1,023 Points

I don't understand the error in this program

the error is: ./com/example/Blog.java:32: error: for-each not applicable to expression type for(String c : 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.

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> categoryCounts = new HashMap<String, Integer>();
    for (BlogPost post : mPosts)  {
     for(String c : post.getCategory() ){

       Integer count = categoryCounts.get(c);
       if ( count == null){
            count = 0;
       }
       count++;
       categoryCounts.put(c,count);
     }
      return categoryCounts;
    }    
  }
}

3 Answers

Alexander Vishnyakov
Alexander Vishnyakov
8,620 Points

Foreach loop takes Collection as a parameter and then iterates through passed Collection. However you are trying to pass a String --> for(String c : post.getCategory() ). post.getCategory() --> returns String. In your case you don't need Foreach loop you can just write --> String c = post.getCategory();

Sara Pasinato
Sara Pasinato
1,023 Points

thanks ? Thanks for you support