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

Rashadat Mirzayev
Rashadat Mirzayev
14,601 Points
Posted by Rashadat Mirzayev
Rashadat Mirzayev
14,601 Points

Too complicated

I made smth like this:

public Map<String, Integer> getCategoryCounts() { Map<String, Integer> getNumbersOfCategory = new HashMap<String, Integer> (); for(BlogPost post: mPosts) { for(String categories: post.getCategory()) { Integer count = getNumbersOfCategory.get(categories); if(count == null) { count = 0; } count++; getNumbersOfCategory.put(categories, count); } } return getNumbersOfCategory;

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.Arrays;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.HashSet;
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> getNumbersOfCategory = new HashMap<String, Integer> ();
      for(BlogPost post: mPosts) {
        for(String categories: post.getCategory()) {
          Integer count = getNumbersOfCategory.get(categories);
          if(count == null) {
          count = 0;
        }
        count++;
        getNumbersOfCategory.put(categories, count);
      }
     }
    return getNumbersOfCategory;
  }  
}

2 Answers

Rashadat Mirzayev
Rashadat Mirzayev
14,601 Points
Rashadat Mirzayev
Rashadat Mirzayev
14,601 Points

Task was: In Blog.java add a new method called getCategoryCounts. It should return a Map of category to count calculated by looping over all the posts.

And after checking this error is showing: ./com/example/Blog.java:35: error: for-each not applicable to expression type for(String categories: 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. 1 error

Abraham Juliot
Abraham Juliot
47,353 Points
Abraham Juliot
Abraham Juliot
47,353 Points

this is unrelated, but near the end, within the nested for loop: if(count == null) { count = 0; // is missing a closing bracket.

Gonzalo Torres del Fierro
PLUS
Gonzalo Torres del Fierro
Courses Plus Student 16,751 Points
Gonzalo Torres del Fierro
Gonzalo Torres del Fierro
Courses Plus Student 16,751 Points

public Map<String, Integer> getCategoryCounts() { Map<String, Integer> categoryCounts = new HashMap<String, Integer>(); for (BlogPost post : mPosts) { String category = post.getCategory(); Integer count = categoryCounts.get(category); if (count == null) { count = 0; } count++; categoryCounts.put(category, count); } return categoryCounts; } }

Gonzalo Torres del Fierro
Gonzalo Torres del Fierro
Courses Plus Student 16,751 Points
Gonzalo Torres del Fierro
Gonzalo Torres del Fierro
Courses Plus Student 16,751 Points

no need 2 times looping, not my solution anyway the owner: Charles Harpke on Apr 19, 2015