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

Posted by pingu
pingu
1,012 Points

Accessing all the categories

I'm not exactly clear on how I could scroll through a list of all the posts' categories.

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.HashMap;
import java.util.Map;

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

1 Answer

Simon Coates
Simon Coates
28,694 Points
Simon Coates
Simon Coates
28,694 Points

i got 

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> elMappo = new HashMap< String ,Integer>();
    for(BlogPost bp: mPosts){
      Integer x = elMappo.get(bp.getCategory());
      if(x==null) {
        elMappo.put(bp.getCategory(), 1);
      }
      else {
        elMappo.put(bp.getCategory(), x +1);
      }
    }
    return elMappo;
  }
}

You need to retrieve the value from the map, and as category is singular, you just need to use it not attempt to iterate (the use of the for loop in your code)