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Java Java Data Structures Exploring the Java Collection Framework Maps

Kevin Lankford
Kevin Lankford
1,940 Points

Not able to access "getCategory" method

I'm wondering why this loop can't access getCategory as it iterates through the BlogPosts. As the for loop iterates through the BlogPost object, can the iterable variable value not access its own methods? Any help is very appreciated. Thank you

./com/example/Blog.java:31: error: for-each not applicable to expression type for (String bp : blog.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

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.HashMap;
import java.util.List;
import java.util.Map;
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 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> catCount = new HashMap<String, Integer>();
      for (BlogPost blog : mPosts) {
        for (String bp : blog.getCategory()) {
          Integer count = catCount.get(bp);
            if (count == null) {
              count = 0;
           }
           count++;
           catCount.put(bp, count);
      }
    }
  }
}

1 Answer

andren
andren
28,521 Points

What make you think it can't access the getCategory method? The error message makes no mention of not being able to access or find the method, it simply states that the for loop is expecting an array or something that is designed to be iterated through, and instead is getting a string, which falls into neither of those categories.

The getCategory method returns a string, not an array or list of strings, just a single string, that is not something a for-each loop can accept, since it is specifically designed to perform actions on a group of items.

If you replace the second for-each loop in your code with:

    String bp = blog.getCategory();

And also add a return statement (which is currently missing) then your code should work fine.