Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

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

Jan Willmann
Jan Willmann
4,387 Points
Posted by Jan Willmann
Jan Willmann
4,387 Points

Why do we need this line of code?

It's the code challange: Maps

Can someone explain me why we need that line of code:

categoryCounts.put(blogPost.getCategory(),counter);

 public Map<String, Integer> getCategoryCounts() {
    Map<String, Integer> categoryCounts = new HashMap<>();

    for (BlogPost blogPost : mPosts) {
      Integer counter = categoryCounts.get(blogPost.getCategory());
      if (counter == null) {
        counter = new Integer(0);
        categoryCounts.put(blogPost.getCategory(), counter);

      }
      counter++;
      categoryCounts.put(blogPost.getCategory(), counter);  // Why do we need this line of code? 
    }
  return categoryCounts;
  }

When is worked here with just using the object reffernce? 

 Map<String, List<Treet>> treetsByAuthor = new HashMap<String, List<Treet>>();

    for (Treet treet : treets) {
      List<Treet> authoredTreets = treetsByAuthor.get(treet.getAuthor());
      if (authoredTreets == null) {
        authoredTreets = new ArrayList<Treet>();
        treetsByAuthor.put(treet.getAuthor(), authoredTreets);
      }
      authoredTreets.add(treet);
    }

Doesn't it work, because "counter" is just a primitive type and "List<>" is an object?