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

Paul Joiner
Paul Joiner
1,682 Points

(Maps video lesson) Example.java won't compile even though I've followed the video step by step. What's going on?

import java.util.Arrays;
import java.util.ArrayList;
import java.util.Date;
import java.util.Set;
import java.util.HashMap;
import java.util.HashSet;
import java.util.TreeSet;
import java.util.List;
import java.util.Map;
import com.teamtreehouse.Treet;
import com.teamtreehouse.Treets;

public class Example {

  public static void main(String[] args) {
    Treet[] treets = Treets.load();
    System.out.printf("There are %d treets. %n",
                     treets.length);
    Set<String> allHashTags = new TreeSet<String>();
    Set<String> allMentions = new TreeSet<String>();
    for (Treet treet : treets) {
      allHashTags.addAll(treet.getHashTags());
      allMentions.addAll(treet.getMentions());
     }
    System.out.printf("Hash tags: %s %n", allHashTags);
    System.out.printf("Mentions: %s %n", allMentions);

    Map<String, Integer> hashTagCounts = new HashMap<String, Integer>();
      for (Treet treet : treets) {
        for (String hashTag : treet.getHashTags()) {
          Integer count = hashTagCounts.get(hashTag);
          if (count == null){
            count = 0;
          }
         count++;
         hashTagCounts.put(hashTag, count);
        }
      }
    System.out.printf("Hash tag counts: %s %n", hashTagCounts);

    Map<String, List<Treet>> treetsByAuthor = new HashMap<String, List<Treet>>();
    for (Treet treet : treets) {
      List<Treets> authoredTreets = treetsByAuthor.get(treet.getAuthor());
      if (authoredTreets == null) {
         authoredTreets = new ArrayList<Treet>();
         treetsByAuthor.put(treet.getAuthor(), authoredTreets);
      }
      authoredTreets.add(treet);
    }
    System.out.printf("Treets by author: %s %n", treetsByAuthor);
    System.out.printf("Treets by nickrp: %s %n", treetsByAuthor.get("nickrp"));

  }

}
Seth Kroger
Seth Kroger
56,413 Points

And what is the error message the compiler gives you?

2 Answers

Seth Kroger
Seth Kroger
56,413 Points
    Map<String, List<Treet>> treetsByAuthor = new HashMap<String, List<Treet>>();
    for (Treet treet : treets) {
      List<Treets> authoredTreets = treetsByAuthor.get(treet.getAuthor());
//-----------^^^ This should be List<Treet> like the rest.
      if (authoredTreets == null) {
         authoredTreets = new ArrayList<Treet>();
         treetsByAuthor.put(treet.getAuthor(), authoredTreets);
      }
      authoredTreets.add(treet);
    }
Paul Joiner
Paul Joiner
1,682 Points

That worked. Thank you!!

Paul Joiner
Paul Joiner
1,682 Points

Example.java:46: error: incompatible types: List<Treets> cannot be converted to List<Treet>
treetsByAuthor.put(treet.getAuthor(), authoredTreets);
^
Example.java:48: error: no suitable method found for add(Treet)
authoredTreets.add(treet);
^
method Collection.add(Treets) is not applicable
(argument mismatch; Treet cannot be converted to Treets)
method List.add(Treets) is not applicable
(argument mismatch; Treet cannot be converted to Treets)

I get the same "incompatible types" error for java lines 43 and 45 but can't copy and paste for some reason