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ISAIAH S
1,409 PointsIn Blog.java add a new method called getCategoryCounts. It should return a Map of category to count calculated by loopin
https://teamtreehouse.com/library/java-data-structures/exploring-the-java-collection-framework/maps-2
I don't know how to 'return a Map of category to count calculated by looping over all the posts'.
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;
}
}
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<>();
for (BlogPost post: mPosts) {
authors.add(post.getAuthor());
}
return authors;
}
}
ISAIAH S
1,409 PointsIn Blog.java add a new method called getCategoryCounts. It should return a Map of category to count calculated by looping over all the posts.
Craig Dennis
Treehouse TeacherYeah that's the question I asked ;) What is your question?
ISAIAH S
1,409 PointsI don't know how to 'return a Map of category to count calculated by looping over all the posts'.
5 Answers
Erik Nilsen
20,433 PointsI'm not sure if this is the optimal way to do it, but here's my solution (only the relevant method is shown). Remember to import any necessary types.
public Map<String, Integer> getCategoryCounts() {
Map<String, Integer> counts = new HashMap<>();
for (BlogPost mPost : mPosts) {
String category = mPost.getCategory();
Integer count = counts.get(category);
if (count == null) count = 0;
count++;
counts.put(category, count)
}
return counts;
}
Erik Nilsen
20,433 PointsNote that count must be an integer object and not a primitive, otherwise the comparison with null will cause a compile-time error.
ISAIAH S
1,409 PointsYour code worked, but how does this work:
if (count == null) count = 0;
Casey Huckel
Courses Plus Student 4,257 PointsI imported Map and HashMap but I still get errors. What are the necessary imports?
Craig Dennis
Treehouse TeacherWatch the Maps video around 8:30. Apart from needing to do the nested for loop, this is very similar to the hashTagCounts.
ISAIAH S
1,409 PointsI don't know what to write.
George Siaskov
1,292 PointsIt cannot find mPost :((
./com/example/BlogPost.java:50: error: cannot find symbol for (BlogPost post : mPost) { ^ symbol: variable mPost
Nicholas Kotsiantos
8,827 Pointspublic Map<String, Integer> getCategoryCounts() { Map<String, Integer> categoryCounts = new HashMap<String, Integer>(); for(BlogPost post : getPosts()) { Integer count = categoryCounts.get(post.getCategory()); if(count == null) { count = 0; } count++; categoryCounts.put(post.getCategory(), count); }
return categoryCounts;
}
I got the answer, but I still do not understand when we do: categoryCounts.get(post.getCategory()); How can you get something if nothing is there yet? We just declared the map, right?
Jebadeiah Jones
10,429 PointsI'm not sure if this is the appropriate place to do this, but I've been stuck on this question for some time now trying to figure out exactly what it was asking of me until I realized that the sentence "It should return a Map of category to count calculated by looping over all the posts," meant "It should return a Map of category-to-count, calculated by looping over all the posts."
I don't think my way of punctuating it is more true, or even grammatically correct, but it emphasizes it in a manner that makes more sense to me. The way it is currently written runs on and I couldn't figure out what it was trying to say.
Craig Dennis
Treehouse TeacherThanks Michael! I'll update it that way! Good suggestion and sorry for the unintended struggle!
Craig Dennis
Treehouse TeacherCraig Dennis
Treehouse TeacherHi Isaiah!
What is your question? It looks like it got chopped off.