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Java Java Data Structures Exploring the Java Collection Framework Maps

Grigorij Schleifer
Grigorij Schleifer
10,365 Points
Posted by Grigorij Schleifer
Grigorij Schleifer
10,365 Points

HashMap error in getCategoryCounts()

Here is my code:

   public Map<BlogPost, Integer> getCategoryCounts(){

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

    for (BlogPost post: mPosts) {
      String category = post.getCategory();
      Integer count = countCategory.get(category);

      if (count == null) {
              count = 0;
        count++;
            }

            countCategory.put(category, count);
       }
  return countCategory;  
   }

and here the error:

./com/example/Blog.java:43: error: incompatible types: Map cannot be converted to Map
  return countCategory;  
         ^
Note: JavaTester.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
1 error

Can someone help me???

1 Answer

Seth Kroger
Seth Kroger
56,413 Points
Seth Kroger
Seth Kroger
56,413 Points

The Map you have declared as the return type is different from the Map you are trying to return. I also see you are incrementing count only if it is null, not for every time you encounter the category.

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

Hi Seth, you are the very best !!!!

Her my code that worked for me :

    public Map<String, Integer> getCategoryCounts(){

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

    for (BlogPost post: mPosts) {
      String category = post.getCategory();
      Integer count = countCategory.get(category);
 if (count == null) {
              count = 0;
            }
            count++;
            countCategory.put(category, count);
       }
  return countCategory;  
   }