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Java Java Data Structures Exploring the Java Collection Framework Sets

Alex Kasper
Alex Kasper
1,896 Points
Posted by Alex Kasper
Alex Kasper
1,896 Points

Java Sets - how do you get the for loop to go through all blogposts?

I'm not entirely sure how to get the for loop to go through all the blog posts. I would imagine that the getPosts method would be doing that but not sure how to get that to work to my advantage.

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;

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> allAuthors = new TreeSet<String>();
    for (getPosts) {
      allAuthors.add(BlogPost.authors);
    }
    return allAuthors;
  }


}

3 Answers

Jeremy Hill
Jeremy Hill
29,567 Points
Jeremy Hill
Jeremy Hill
29,567 Points

I believe your for loop needs to look like this:

for(BlogPost blogPost : mPosts)

Then just reference the variable "blogPost" or whatever you name it.

Alex Kasper
Alex Kasper
1,896 Points
Alex Kasper
Alex Kasper
1,896 Points

Thanks for the help. I'm still not able to pass the challenge. 

package com.example;

import java.util.List;
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> allAuthors = new TreeSet<String>();
    for (BlogPost blogPost : mPosts) {
      allAuthors.add(blogPost.author);
    }
    return allAuthors;
  }
}

The compiler is saying that it can't find the author variable. Is there a reason behind this?

Also I don't fully comprehend what this code dose

for (BlogPost blogPost : mPosts)

the for is enabling the for loop. The BlogPost blogPost is creating a object of BlogPost called blogPost. What is the is : mPosts doing?

Florian Tönjes
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Florian Tönjes
Full Stack JavaScript Techdegree Graduate 50,856 Points
Florian Tönjes
.a{fill-rule:evenodd;}techdegree seal-36
Florian Tönjes
Full Stack JavaScript Techdegree Graduate 50,856 Points

The compiler cannot find the 'author' variable because it does not exist. The BlogPost object does have an 'mAuthor' variable, but this variable is private and can only be accessed from outside using the 'getAuthor' getter method.

  public Set<String> getAllAuthors() {
    Set<String> allAuthors = new TreeSet<>();
    for (BlogPost blogPost : mPosts) {
      allAuthors.add(blogPost.getAuthor());  // Now using the getAuthor() getter.
    }
    return allAuthors;
  }

This code

for (BlogPost blogPost : mPosts) { 
// Compound statement
}

means:

Execute the compound statement for each element of the 'mPosts' list. Assign one of the elements to the variable named 'blogPost', which is of type BlogPost, on each loop pass.

Regards, Florian

Alex Kasper
Alex Kasper
1,896 Points
Alex Kasper
Alex Kasper
1,896 Points

Thanks for the breakdown Florian! That really helped clear up a bunch, a new deeper understanding of the private variable. Now I really get what the getters are for.

Jeremy Hill
Jeremy Hill
29,567 Points
Jeremy Hill
Jeremy Hill
29,567 Points

Here try this:

package com.example;

import java.util.List;
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<String>();
    for(BlogPost post : mPosts){
      authors.add(post.getAuthor());
    }
    return authors;
  }
}