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

Casey Huckel
PLUS
Casey Huckel
Courses Plus Student 4,257 Points
Posted by Casey Huckel
Casey Huckel
Courses Plus Student 4,257 Points

What's missing here?

Get 7 errors here and don't know why. I'll post compilation errors in addition to code.

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.Map;
import java.util.HashMap;
import java.util.Date;
import java.util.HashSet;

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;
}

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;
  }
}
Casey Huckel
Casey Huckel
Courses Plus Student 4,257 Points
Casey Huckel
Casey Huckel
Courses Plus Student 4,257 Points

Here's a list of errors:

./com/example/Blog.java:13: error: class, interface, or enum expected public Map getCategoryCounts() { ^ ./com/example/Blog.java:15: error: class, interface, or enum expected for (BlogPost mPost : mPosts) { ^ ./com/example/Blog.java:17: error: class, interface, or enum expected Integer count = counts.get(category); ^ ./com/example/Blog.java:18: error: class, interface, or enum expected if (count == null) count = 0; ^ ./com/example/Blog.java:19: error: class, interface, or enum expected count++; ^ ./com/example/Blog.java:20: error: class, interface, or enum expected counts.put(category, count) ^ ./com/example/Blog.java:23: error: class, interface, or enum expected } ^ Note: JavaTester.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details. 7 errors

1 Answer

Grigorij Schleifer
Grigorij Schleifer
10,365 Points
Grigorij Schleifer
Grigorij Schleifer
10,365 Points

Hi Casey,

delete the second imports of Map and HashMap.

Let us look at your code:

 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) { // added a curly bracket to open the if loop
          count = 0;
    }
    count++;
    counts.put(category, count); // added a semicolon here
  } // added a curly bracker to close the for loop
    return counts;
}

You was incrementing count only if it is null, not for every time you encounter the category. And you added category + count if the count was null. So I moved 

count++;
counts.put(category, count);

out of the if statement.

I hope it help you a little bit.

Grigorij

Jordan Ernst
Jordan Ernst
5,121 Points
Jordan Ernst
Jordan Ernst
5,121 Points

don't forget >> 

Map<String, Integer> counts= new HashMap<String, Integer>();